Micro mirror device

ABSTRACT

The present invention provides a mirror device, comprising: an electrode placed on a substrate; a memory circuit connected to the electrode; an elastic hinge disposed near said electrode and extending from said substrate for supporting a mirror above said electrode wherein said elastic hinge having a negative temperature coefficient of resistance.

This application is a Continuation in Part (CIP) application of aCo-Pending patent application Ser. No. 11/894,248 filed on Aug. 18, 2007by one of common Inventors of this patent application. Application Ser.No. 11/894,248 is a Non-provisional application of a ProvisionalApplication 60/841,173 filed on Aug. 30, 2006. The Non-provisionalapplication Ser. No. 11/894,248 is a Continuation in Part (CIP)application of U.S. patent application Ser. No. 11/121,543 filed on May4, 2005, now issued into U.S. Pat. No. 7,268,932. The application Ser.No. 11/121,543 is a Continuation in part (CIP) application of threepreviously filed applications. These three applications are Ser. Nos.10/698,620; 10/699,140, now issued into U.S. Pat. No. 6,862,127; and10/699,143, now issued into U.S. Pat. No. 6,903,860. All three patentswere filed on Nov. 1, 2003 by one of the Applicants of this patentapplication. The disclosures made in these patent applications arehereby incorporated by reference in this patent application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image display apparatus implementedwith a mirror device for modulating light. More particularly, thisinvention relates to an image display apparatus implemented with amirror device comprises mirror elements each includes an elastic hingemanufactured with special structure for supporting the mirror.

2. Description of the Related Art

Even though there are significant advances of the technologies forimplementing an electromechanical mirror device as a spatial lightmodulator (SLM) in recent years, there are still limitations anddifficulties when current technologies according to the state of the artare applied to provide a high quality image. Specifically, when theimages are digitally controlled, the image quality is adversely affecteddue to the limitation that the images are not displayed with sufficientnumber of gray scales.

An electromechanical mirror device is drawing a considerable interestand commonly employed as a spatial light modulator (SLM) in the imageproject apparatuses. The electromechanical mirror device is typicallyimplemented with a “mirror array” comprising a large number of mirrorelements. In general, the number of mirror elements may range from60,000 to several millions of micromirror pieces are manufactured astwo-dimensional array on a surface of a substrate in anelectromechanical mirror device.

Referring to FIG. 1A for an image display system 1 disclosed in U.S.Pat. No. 5,214,420 that comprises a screen 2. The display system 1further includes a light source 10 to project an illumination light fordisplaying images on the screen 2. The illumination light 9 from thelight source is further focused and directed toward a lens 12 by amirror 11. Lenses 12, 13, and 14 function together as a beam culminatorto culminate light 9 into a culminated light 8. A spatial lightmodulator (SLM) 15 is controlled on the basis of data input by acomputer 19 via a bus 18 to selectively redirect portions of light froma path 7 toward an enlarger lens 5 and onto screen 2. The SLM 15 isimplemented with a mirror array comprising large number of mirror 33each includes a deflectable reflective element shown as elements 17, 27,37, and 47 depicted in FIG. 1B. Each mirror 33 is connected by a hinge30 on a surface 16 of a substrate in the electromechanical mirror deviceas shown in FIG. 1B. When the element 17 is in one position, a portionof the light from the path 7 is redirected along a path 6 to lens 5where it is enlarged or spread along the path 4 to impinge on the screen2 to display an illuminated pixel 3. When the element 17 is in anotherposition, the light is redirected away from screen 2 and hence the pixel3 is displayed as a dark pixel on the display screen 2.

The mirror device comprises a plurality of mirror elements to functionas spatial light modulator (SLM) wherein each mirror element comprises amirror and electrodes. A voltage applied to the electrode(s) generates acoulomb force between the mirror and the electrode(s) to control themirror to tilt to an inclined angle. According to a common term used inthis specification, the mirror is “deflected” to an angular position fordescribing the operational condition of a mirror element.

When a voltage applied to the electrode(s) controls the mirror todeflect to a controlled angular position, the deflected mirror alsoreflects an incident light to a controlled direction. The direction ofthe reflected light is therefore controlled in accordance with thedeflection angle of the mirror and that in turn is controlled by avoltage applied to the electrode. The present specification refers to astate of the mirror as an ON state when the mirror reflectssubstantially the entirety of an incident light a projection pathdesignated for image display and as an OFF state when the mirrorreflects the incident light to a direction away from the designatedprojection path for image display.

Furthermore, there is a specific ratio of an amount of light reflectedto the display screen by the mirror operated in an ON state relative toan amount of light reflected by the mirror operated at an OFF state.Furthermore, an “Intermediate state” is referred to a condition when themirror reflects an amount of light to the projection path that issmaller than the amount of light of the ON state but greater than theamount of light of the OFF state.

The terminology of present specification defines an angle of rotationalong a clockwise (CW) direction as a positive (+) angle and that ofcounterclockwise (CCW) direction as negative (−) angle. A deflectionangle is defined as zero degree (0°) when the mirror is in the initialstate with no voltage applied to the electrode to function as areference of mirror deflection angle.

Most of the conventional image display devices such as the devicesdisclosed in U.S. Pat. No. 5,214,420 implements a dual-state mirrorcontrol technique that controls the mirrors in a state of either ON orOFF. The quality of an image display is limited due to the limitednumber of gray scales when the mirrors are controlled to operate only atan ON or OFF states. Specifically, in a conventional control circuitthat applies a PWM (Pulse Width Modulation), the quality of the image islimited by the LSB (least significant bit) or the least pulse width as aminimum length of time that a mirror can be controlled to operate in anON or OFF state. Since the mirror is controlled to operate in either theON or OFF state, the conventional image display apparatus is limited bythe LSB and not able to operate the mirror with a pulse width shorterthan the control duration allowable based on the LSB. The least amountof controllable light defines the resolution of the gray scale isdetermined by the light reflected during the time duration based on theleast pulse width. The limited number of gray scales thus leads to adegradation of the quality of the displayed image.

Specifically, FIG. 1C exemplifies a control circuit for controlling amirror element according to the disclosure in the U.S. Pat. No.5,285,407. The control circuit includes a memory cell 32. Varioustransistors are referred to as “M*” where “*” designates a transistornumber and each transistor is an insulated gate field effect transistor.Transistors M5 and M7 are p-channel transistors; while transistors M6,M8, and M9 are n-channel transistors. The capacitances C1 and C2represent the capacitive loads in the memory cell 32. The memory cell 32includes an access switch transistor M9 and a latch 32 a, which is basedon a typical Static Random Access switch Memory (SRAM) design. Thetransistor M9 connected to a Row-line receives a data signal via aBit-line. The memory cell 32 written data is accessed when thetransistor M9 which has received the ROW signal on a Word-line is turnedon. The latch 32 a consists of two cross-coupled inverters, i.e., M5/M6and M7/M8, which permit two stable states, that is, a state 1 is Node Ahigh and Node B low, and a state 2 is Node A low and Node B high.

The mirror is driven by a voltage applied to the address electrodeconnected to an address electrode and is held at a predetermineddeflection angle on the address electrode. An elastic “landing chip” isformed at a portion on the address electrode, which makes the addresselectrode contact with mirror, and assists the operation for deflectingthe mirror toward the opposite direction when a deflection of the mirroris switched. The landing chip is designed as having the same potentialwith the address electrode, so that an electric short circuit isprevented when the address electrode is in contact with the mirror.

Each mirror formed on a device substrate has a square or rectangularshape and each side has a length of 4 to 15 μm. In this configuration, areflected light that is not controlled for purposefully applied forimage display may however inadvertently generated by reflections throughthe gap between adjacent mirrors. The contrast of an image displaygenerated by adjacent mirrors is degraded due to the reflectionsgenerated not by the mirrors but by the gaps between the mirrors. As aresult, a quality of the image display is adversely affected due to areduced contrast. In order to overcome such problems, the mirrors arearranged on a semiconductor wafer substrate with a layout to minimizethe gaps between the mirrors. One mirror device is generally designed toinclude an appropriate number of mirror elements wherein each mirrorelement is manufactured as a deflectable mirror on the substrate fordisplaying a pixel of an image. The appropriate number of elements fordisplaying image is in compliance with the display resolution standardaccording to a VESA Standard defined by Video Electronics StandardsAssociation or television broadcast standards. In the case in which themirror device has a plurality of mirror elements corresponding to WideeXtended Graphics Array (WXGA), whose resolution is 1280 by 768, definedby VESA, the pitch between the mirrors of the mirror device is 10 μm andthe diagonal length of the mirror array is about 0.6 inches.

The control circuit, as illustrated in FIG. 1C, controls themicromirrors to switch between two states, and the control circuitdrives the mirror to oscillate to either an ON or OFF deflection angle(or position) as shown in FIG. 1A.

The minimum intensity of light controllable to reflect from each mirrorelement for image display, i.e., the resolution of gray scale of imagedisplay for a digitally controlled image display apparatus, isdetermined by the least length of time that the mirror is controllableto be held in the ON position. The length of time that each mirror iscontrolled to be held in an ON position is in turn controlled bymultiple bit words.

FIG. 1D shows the “binary time periods” in the case of controlling theSLM by four-bit words. As shown in FIG. 1D, the time periods haverelative values of 1, 2, 4, and 8 that in turn determine the relativeintensity of light of each of the four bits, where “1” is the leastsignificant bit (LSB) and “8” is the most significant bit. According tothe PWM control mechanism, the minimum intensity of light thatdetermines the resolution of the gray scale is a brightness controlledby using the “least significant bit” which holds the mirror at an ONposition for the shortest controllable length of time.

For example, assuming n bits of gray scales, one time frame is dividedinto 2^(n)−1 equal time periods. For a 16.7-millisecond frame period andn-bit intensity values, the time period is 16.7/(2^(n)−1) milliseconds.

Having established these times for each pixel of each frame, pixelintensities are quantified such that black is a 0 time period, theintensity level represented by the LSB is 1 time period, and the maximumbrightness is 2^(n)−1 time periods. Each pixel's quantified intensitydetermines its ON-time during a time frame. Thus, during a time frame,each pixel with a quantified value of more than 0 is ON for the numberof time periods that correspond to its intensity. The viewer's eyeintegrates the pixel brightness so that the image appears the same as ifit were generated with analog levels of light.

For controlling deflectable mirror devices, the PWM applies data to beformatted into “bit-planes”, with each bit-plane corresponding to a bitweight of the intensity of light. Thus, if the brightness of each pixelis represented by an n-bit value, each frame of data has then-bit-planes. Then, each bit-plane has a 0 or 1 value for each mirrorelement. According to the PWM control scheme described in the precedingparagraphs, each bit-plane is independently loaded and the mirrorelements are controlled according to bit-plane values corresponding tothe value of each bit during one frame. Specifically, the bit-planeaccording to the LSB of each pixel is displayed for 1 time period.

When adjacent image pixels are displayed with a very coarse gray scalecaused by great differences in the intensity of light, thus, artifactsare shown between these adjacent image pixels. That leads to thedegradations of image quality. The image degradations are especiallypronounced in the bright areas of image where there are “bigger gaps”between of the gray scales of adjacent image pixels. The artifacts aregenerated by technical limitations in that the digitally controlledimage does not provide a sufficient number of the gray scale.

As the mirrors are controlled to operate in a state of either ON or OFF,the intensity of light of a displayed image is determined by the lengthof time each mirror is in the ON position. In order to increase thenumber of gray scales of a display, the switching speed of the ON andOFF positions for the mirror must be increased. Therefore the digitalcontrol signals need be increased to a higher number of bits. However,when the switching speed of the mirror deflection is increased, astronger hinge for supporting the mirror is necessary to sustain therequired number of switches between the ON and OFF positions for themirror deflection. In order to drive the mirrors with a strengthenedhinge, a higher voltage is required. The higher voltage may exceedtwenty volts and may even be as high as thirty volts. The mirrorsproduced by applying the CMOS technologies are probably not appropriatefor operating the mirror at such a high range of voltages, and thereforeDMOS mirror devices may be required. In order to achieve a higher degreeof gray scale control, more complicated production processes and largerdevice areas are required to produce the DMOS mirror. Conventionalmirror controls are therefore faced with a technical problem in thataccuracy of gray scales and range of the operable voltage have to besacrificed for the benefits of a smaller image display apparatus.

There are many patents related to light intensity control. These patentsinclude U.S. Pat. Nos. 5,589,852, 6,232,963, 6,592,227, 6,648,476, and6,819,064. There are further patents and patent applications related todifferent light sources. These patents include U.S. Pat. Nos. 5,442,414,6,036,318 and Application 20030147052. Also, U.S. Pat. No. 6,746,123 hasdisclosed particular polarized light sources for preventing the loss oflight. However, these patents or patent applications do not provide aneffective solution to attain a sufficient number of the gray scale inthe digitally controlled image display system.

Furthermore, there are many patents related to a spatial lightmodulation including U.S. Pat. Nos. 2,025,143, 2,682,010, 2,681,423,4,087,810, 4,292,732, 4,405,209, 4,454,541, 4,592,628, 4,767,192,4,842,396, 4,907,862, 5,214,420, 5,287,096, 5,506,597, and 5,489,952.However, these inventions do not provide a direct solution for a personskilled in the art to overcome the above-discussed limitations anddifficulties.

In view of the above problems, US Patent Application 20050190429 hasdisclosed a method for controlling the deflection angle of the mirror toexpress higher gray scales of an image. In this disclosure, theintensity of light obtained during the oscillation period of the mirroris about 25% to 37% of the intensity of light obtained while the mirroris held in the ON position continuously.

According to this control process, it is not necessary to drive themirror at a high speed. Also, it is possible to provide a higher numberof the gray scale using a hinge with a low elastic constant. Hence, sucha control makes it possible to reduce the voltage applied to the addresselectrode.

An image display apparatus using the mirror device described above isbroadly categorized into two types: a single-plate image displayapparatus implemented with only one spatial light modulator and amulti-plate image display apparatus implemented with a plurality ofspatial light modulators. In the single-plate image display apparatus, acolor image is displayed by changing, in turn, the color (i.e. frequencyor wavelength) of projected light over time. In a multi-plate the imagedisplay apparatus, a color image is displayed controlling the multiplespatial light modulators, corresponding to beams of light havingdifferent colors (i.e. frequencies or wavelengths), to modulate andcombine the beams of light continuously.

For projection apparatuses there has been an increasing demand forhigh-resolution definitions, such as a full high definition (Full-HD;1920×1080 pixels) television these days, prompting the development ofhigher resolution display techniques.

A mirror device is usually the spatial light modulator used for such aprojection apparatus. The mirror device is comprised of a mirror arrayof two to eight million mirror-elements in two dimensions on a devicesubstrate.

The size of a mirror of the mirror element of a common mirror device is11 μm square. A memory cell for driving the mirror is comprised withinthe substrate. Further, the mirror is controlled by setting theoperating voltage of the memory cell, or the drive voltage fordeflecting the mirror, to “5” volts or higher. Further, such a mirror isgenerally supported by an elastic hinge.

A common mirror device used for high definition (Full-HD) has thediagonal size of 24.13 mm (0.95 inches), with a mirror pitch of 11 μm.An XGA-size mirror device has the diagonal size of 17.78 mm (0.7 inches)of the mirror array, with the mirror pitch of 14 μm.

FIG. 2 is a diagonal view of a mirror device arraying, in two-dimensionon a device substrate, mirror elements controlling a reflectiondirection of incident light by deflecting the mirror.

The mirror device 200 shown in FIG. 2 is constituted by arraying aplurality of mirror elements 300, each of which is constituted by anaddress electrode (not shown in the drawing herein), elastic hinge (notshown) and a mirror supported by the elastic hinge, lengthwise andcrosswise (i.e., in two-dimension) on a device substrate 303.

FIG. 2 illustrates the case of arraying a plurality of mirror elements300 comprising square mirrors 302 lengthwise and crosswise at equal gapson the device substrate 303.

The mirror 302 can be controlled by applying a voltage to the addresselectrode provided on the device substrate 303. In FIG. 2, a deflectionaxis 201 for deflecting the mirror 302 is indicated by the dotted line.The light emitted from a light source 301 is incident to the mirror 302so as to be orthogonal or diagonal relative to the deflection axis 201.

Specifically, in the present specification document, the distancebetween the deflection axes 201 of mutually adjacent mirrors 302 istermed as “pitch” and the distance between the mutually adjacent mirrors302 is termed as “gap”.

The following is a description of an operation of the mirror element 300by referring to the cross-sectional line II-II of the mirror element 300of the mirror device 200 shown in FIG. 2.

FIGS. 3A and 3B are cross-sectional diagrams of the line II-II indicatedin FIG. 2.

The mirror element 300 comprises a mirror 302, an elastic hinge 304 forsupporting mirror 302, two address electrodes 307 a and 307 b, whichplaced opposite mirror 302, and a first and second memory cell, both forapplying a voltage to the address electrodes 307 a and 307 b in order tooperate the mirror 302 under a controllable deflection state.

The drive circuits for each of the memory cells are commonly placedinside the device substrate 303 to control each memory cell by thesignal according to the image data thus controlling the deflection angleof mirror 302 for reflecting and modulating the incident light.

FIG. 3A is a cross-sectional diagram for illustrating an ON state of amirror element 300 when the deflectable mirror 302 reflects the incidentlight to a projection optical system.

A signal [0, 1] applied to a memory cell represents a voltage “V=0”applied to the address electrode 307 a on one side and another voltageV=Va applied to the address electrode 307 b on the other side. As aresult, a Coulomb force is generated by the voltage Va applied to theelectrode 307 b to draw the mirror 302 to deflect from a horizontalstate to incline to the direction of the address electrode 307 b . . . .The mirror 302 is controlled to operate in an ON state to reflect theincident light emitted from a light source 301 to the projection opticalsystem. Specifically an insulation layer 306 is formed to cover over thedevice electrode, i.e., the address electrodes 307 a and 307 b, and ahinge electrode 305 connected to the elastic hinge 304 is groundedthrough a Via connector not shown in a drawing formed in insulationlayer 306.

FIG. 3B is a cross-sectional diagram for illustrating an OFF state of amirror element 300 when the deflectable mirror 302 reflects the incidentlight away from the projection optical system.

A signal [1, 0] applied to a memory cell represents a voltage V=Vaapplied to the address electrode 307 a on one side and another voltage“V=0” applied to the address electrode 307 b on the other side. As aresult, a Coulomb force is generated by the voltage Va applied to theelectrode 307 a to draw the mirror 302 to deflect from a horizontalstate to incline to the direction of the address electrode 307 a. Themirror 302 is controlled to operate in an OFF state to reflect theincident light outside of the light path projecting to the projectionoptical system.

Specifically, the Coulomb force generated between the mirror 302 andaddress electrode 307 a, or 307 b, may be represented by the followingexpression:

$F = {k^{\prime}\frac{{eS}^{2}X^{2}}{2h^{2}}}$

(1);

where “S” is the area of the address electrode 307 a or 307 b, “h” isthe distance between the mirror 302 and address electrode 307 a or 307b, “e” is the permittivity between the mirror 302 and address electrode307 a or 307 b, “V” is the voltage applied to the address electrode 307a or 307 b, and “k′” is a correction coefficient.

FIG. 4 is a cross-sectional diagram illustrating the reflection ofincident light onto a mirror device 200.

Each of the mirror elements 300 in the mirror device 200 shown in FIG. 4comprises a mirror 302 and hinge 304 juxtaposed on the device substrate303 enclosed in a package 308. The package 308 is formed with a shape ofa hollow rectangle with an open top, and the top is covered with a coverglass 309, which allows the transmission of light.

The mirror device as described above can be produced through the sameprocesses as commonly applied in the production process of asemiconductor device. The production processes mainly includesprocessing steps of chemical vapor deposition (CVP), photolithography,etching, doping, and chemical mechanical polishing (CMP).

Practically, in order to respond to a higher resolution of the imageprojected in a projection apparatus, the number of mirror elements mustbe increased, requiring a reduction in size of the mirror of the mirrorelement.

A reduction in mirror size necessitates an elastic hinge that isextremely thin and small, having a thickness ranging from 100- to 1000angstrom and having a width ranging from 1.2- to 0.3 μm. This requiresthat the area for fixing the elastic hinge onto the address electrodebecomes very small, making it very difficult to fix the elastic hingesecurely so as to prevent the hinge from being detached by an elasticforce applied to its base. Furthermore, in the case of a perpendicularelastic hinge, it functions as a cantilevered spring, which is fixedonly at the base, which endures a large force.

Additionally, in the processes of forming an elastic hinge, the etchingis repeated, and therefore precautions must be taken to prevent the baseof the hinges or regions near the bottom portions of the elastic hingefrom being cut or corroded. Specifically, there are additionaldifficulties due to the facts that when the sacrifice layer is made ofsilicon dioxide (SiO₂), hydrogen fluoride (HF) is used as etchant, thebase and the lower portions as fixed part of an elastic hinge may easilybe exposed and damaged and/or corroded. Therefore, the currenttechnologies of manufacturing the mirror devices implemented as thespatial light modulator is confronted with difficulties and limitations.Such limitations and difficulties are still not resolved by theabove-discussed patents and disclosures and further in view of theadditional patents as listed below.

The following patents are related to the structures of the conventionalmirror devices and the techniques for producing the mirror devices. U.S.Pat. No. 7,183,618 discloses a hinge formed in the opening part of apedestal. U.S. Pat. No. 7,273,693 discloses a mirror device comprising amirror support. U.S. Pat. Nos. 5,673,139; 6,128,121; and 7,068,417disclose a vertical hinge. U.S. Pat. No. 7,022,249 discloses a methodfor forming the base of a hinge and U.S. Pat. No. 5,497,262 discloses ahorizontal hinge structure. However these disclosures have not disclosedconfigurations or manufacturing methods to overcome the above-discusseddifficulties or limitations.

SUMMARY OF THE INVENTION

One aspect of the present invention is to provide a mirror device withhinges robustly, securely and reliably attached to the device substratesuch that the limitations and difficulties of the conventionaltechnologies can be resolved. Another aspect of the present invention isto provide a mirror device to achieve a higher level of definition of animage.

A first aspect of the present invention provides a mirror device,comprising: an electrode placed on a substrate; a memory circuitconnected to the electrode; an elastic hinge disposed near saidelectrode and extending from said substrate for supporting a mirrorabove said electrode wherein said elastic hinge having a negativetemperature coefficient of resistance.

A second aspect of the present invention provides the mirror deviceaccording to the first aspect, wherein the elastic hinge furthercomprises a silicon material containing at least an additive selectedfrom materials consist of either a group-III atom or a group-V atom.

A third aspect of the present invention provides the mirror deviceaccording to the first aspect, wherein the elastic hinge furthercomprises a silicon material containing an additive and having aresistance approximately 1 giga-ohms or less.

A fourth aspect of the present invention provides the mirror deviceaccording to the first aspect, wherein the elastic hinge is formed byapplying a chemical vapor deposition (CVD) fabrication process on saidsubstrate.

A fifth aspect of the present invention provides the mirror deviceaccording to the first aspect, wherein the elastic hinge furthercomposed of a metallic material migrating from said electrode or mirror.

A sixth aspect of the present invention provides the mirror deviceaccording to the first aspect, wherein the elastic hinge has smallercross-sectional area near said mirror than a cross sectional area of anopposite end near said substrate.

A seventh aspect of the present invention provides a mirror device,comprising: a stationary electrode disposed on a substrate; a movableelectrode disposed at a distance away from the stationary electrode; anelastic hinge extended from said substrate for supporting the movableelectrode; and a drive circuit for applying adjustable voltages to thestationary electrode or movable electrode to control the movableelectrode, wherein the drive circuit controls the movable electrode tooperate with a time sequence depending on an electric resistance of theelastic hinge.

An eighth aspect of the present invention provides the mirror deviceaccording to the seventh aspect, the timing of the drive circuitcontrols the time sequence of an operation of the movable electrode.

A ninth aspect of the present invention provides the mirror deviceaccording to the seventh aspect, wherein the elastic hinge furthercomprises a silicon (Si) material doped with a material selected from agroup of materials consisted of ε either of a group-III atom and group-Vatom.

A tenth aspect of the present invention provides the mirror deviceaccording to the seventh aspect wherein an anti-stiction coating appliedto cover at least either of the movable electrode or stationaryelectrode for preventing a stiction of a mirror to either said movableelectrode or said stationary electrode.

An eleventh aspect of the present invention provides a mirror device,comprising: a plurality of electrodes placed on a substrate; a mirrorplaced at a distance away from the electrode; and an elastic hingedisposed between the mirror and electrode, wherein the elastic hinge hasa smaller resistance in an operational temperature or operating themirror device than a normal ambient temperature.

A twelfth aspect of the present invention provides the mirror deviceaccording to the eleventh aspect wherein the operational temperature foroperating the mirror device is approximately 50° C. or higher and theelectric resistance of the elastic hinge is approximately 0.5 giga-ohmsor less.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in detail below with reference to thefollowing Figures.

FIG. 1A is a functional block diagram for showing shows a projectiondisplay system using a micromirror device.

FIG. 1B is a top view for showing a micromirror device implemented in aprojection display system of FIG. 1A.

FIG. 1C is a circuit diagram for showing an exemplary driving circuit ofrelated arts.

FIG. 1D is a diagram for showing the scheme of Binary Pulse WidthModulation (Binary PWM) of a conventional digital micromirror togenerate grayscale.

FIG. 2 is a diagonal view of a mirror device comprising two-dimensionarray of mirror elements on a device substrate for controlling thereflection direction of incident light by deflecting the mirror.

FIG. 3A is a cross-sectional diagram of a mirror element reflectingincident light to a projection optical system (i.e., an ON light state)by deflecting the mirror.

FIG. 3B is a cross-sectional diagram of a mirror element reflecting theincident light away from the projection optical system (i.e., an OFFlight state) by deflecting the mirror.

FIG. 4 is a cross-sectional diagram illustrating the incident light to amirror device.

FIG. 5A is a cross-sectional diagram illustrating the method formanufacturing a mirror device according to a preferred embodiment of thepresent invention (part 1).

FIG. 5B is a cross-sectional diagram illustrating the method formanufacturing a mirror device according to a preferred embodiment of thepresent invention (part 2).

FIG. 5C is a cross-sectional diagram illustrating the method formanufacturing a mirror device according to a preferred embodiment of thepresent invention (part 3).

FIG. 5D is a cross-sectional diagram illustrating the method formanufacturing a mirror device according to a preferred embodiment of thepresent invention (part 4).

FIG. 5E is a cross-sectional diagram illustrating the method formanufacturing a mirror device according to a preferred embodiment of thepresent invention (part 5).

FIG. 5F is a cross-sectional diagram illustrating the method formanufacturing a mirror device according to a preferred embodiment of thepresent invention (part 6).

FIG. 6A is a top perspective view diagram showing a mirror element.

FIG. 6B is a side cross sectional view diagram of a mirror element.

FIG. 7A is a cross-sectional diagram of a mirror element.

FIG. 7B is a top view diagram showing the surface of the semiconductorwafer substrate of a mirror element.

FIG. 7C is a partial plain view diagram showing a modified example inwhich the surface electrode shown in FIG. 7B is changed to a pluralityof surface electrodes.

FIG. 7D is a plain view diagram showing a mirror element excluding amirror.

FIG. 7E is a cross-sectional diagram illustrating the ON state of amirror element.

FIG. 7F is a cross-sectional diagram illustrating the OFF state of amirror element.

FIG. 7G is a functional diagram showing an exemplary configuration of acircuit for the mirror element shown in FIG. 7A.

FIG. 7H is a circuit diagram showing an example of a modification ofFIG. 7G.

FIG. 7I is a circuit diagram showing the equivalent circuit of theconfiguration of the mirror element illustrated in FIG. 7G.

FIG. 7J is a timing diagram illustrating a relationship between theapplication timing of a hinge potential from a hinge line and thedeflecting operation of a mirror according to a preferred embodiment ofthe present invention.

FIG. 7K is a timing diagram showing a case in which the polarity of thedrive voltage for a mirror is reverse to that of FIG. 7J.

FIG. 7L is a timing diagram showing an example of a modification of thedeflection control for the mirror illustrated in FIG. 7J.

FIG. 7M is a circuit diagram showing an example of a modification of thecircuit configuration illustrated in FIG. 7G.

FIG. 7N is a circuit diagram showing an equivalent circuit in a case inwhich a mirror is on an OFF side in the circuit configurationillustrated in FIG. 7M.

FIG. 7O is a timing diagram showing an example of a function of thecircuit configuration illustrated in FIGS. 7M and 7N.

FIG. 7P is a diagram showing the temperature characteristic of theelectrical resistance of a material constituting an elastic hingeaccording to a preferred embodiment of the present invention.

FIG. 7Q is a diagram showing an example of a method for expressing grayscales utilizing a horizontal stationary state of a mirror in additionto an operation for deflecting it to ON/OFF states.

FIG. 7R is a perspective diagram showing the relationship betweenincident light/reflection and aperture stop when a mirror is shiftedbetween the ON, intermediate, and OFF states.

FIG. 7S is a timing diagram showing a mirror displacement profile in thecase of applying, to a color display, a gray scale control by means of adeflection control, including the horizontal stationary state of amirror illustrating in FIG. 7Q.

FIG. 8 is a functional block diagram showing a single-plate projectionapparatus comprising one mirror device.

FIG. 9A is a front view diagram showing a two-plate projection apparatuscomprising two mirror devices.

FIG. 9B is a rear view diagram showing a two-plate projection apparatus.

FIG. 9C is a side view diagram showing a two-plate projection apparatus.

FIG. 9D is a top view, diagram showing a two-plate projection apparatus.

FIG. 10 is a functional block diagram showing a three-plate projectionapparatus comprising three mirror devices.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a description of a mirror device and projectionapparatus according to a preferred embodiment of the present inventionby referring to the accompanying drawings.

FIGS. 5A through 5F are cross-sectional diagrams illustrating the methodfor manufacturing a mirror device according to a preferred embodiment ofthe present invention.

As shown in FIG. 5A, the wiring 502 of a drive circuit for driving andcontrolling a mirror (which is described later) is placed inside asemiconductor wafer substrate (simply noted as “substrate” hereafter)501 shown in step 1.

Specifically, an opening (i.e., a cavity or concave part) 501 a contactsthe upper surface of wiring 502 is formed on the upper surface of thesubstrate 501, and the periphery (excluding opening 501 a of the uppersurface), side and bottom surfaces of wiring 502 are covered with asubstrate (i.e., an insulation layer on the substrate) 501. Specificallywiring 502 is preferably made of aluminum.

Furthermore, a first protective layer (i.e., a protective film) 503 isdeposited on the parts of the substrate 501 (shown in step 1) except forthe opening 501 a. The first protective layer 503 is deposited beforethe opening 501 a of the substrate 501 is formed, and therefore anopening 503 a of the same area as opening 501 a is also formed on thefirst protective layer 503. The first protective layer 503 is a layerfor preventing wiring 502 from being corroded with hydrogen fluoride(HF) when the sacrifice layer (which is described later) is removed byan etchant HF.

Specifically, the substrate 501 shown in FIGS. 5A through 5F includesonly an insulation layer deposited on the upper part of the siliconsubstrate. The insulation layer and first protective layer 503 each ispreferably a layer which has structure that may comprise amorphoussilicon, a double-layer structure consisting of amorphous silicon andsilicon carbide (SiC), and which includes silicon such as siliconcarbide (SiC) and silicon dioxide (SiO₂).

In step 2-1, an electrode 504 is formed on the first protective layer503 with the openings 501 a and 503 a at the center. In this process,the electrode 504 is deposited also on the openings 501 a and 503 a, andtherefore a concave opening (i.e., a cavity or an opening from the topof the substrate) 504 a is formed on the upper surface and at the centerof the electrode 504. Specifically, the electrode 504 is preferablyconnected to a micro-electrical mechanical system (MEMS) structure thatcorresponds three-dimensionally (that is, corresponding in differentplural surfaces in the case of a face to face connection). The presentembodiment is configured such that an elastic hinge (which is describedlater) formed by applying a micro electromechanical system) MES)technology as a MEMS structure. Furthermore, the electrode 504 isconnected to one end of the elastic hinge (i.e., a part of the sidesurface of the elastic hinge and the bottom surface thereof according tothe present embodiment) as a MEMS structure.

In an exemplary embodiment the electrode 504 is fabricated with aluminumcontaining silicon (Si) to prevent an occurrence of migration betweenthe electrode 504 and the elastic hinge. Specifically, the electrode 504functions as base for fixing the elastic hinge, which is described indetail below.

Particularly, when aluminum is used for the electrode 504, and amorphoussilicon is used for the insulation layer and the first protective layer503, the aluminum-made electrode 504 is corroded if the aluminum-madeelectrode 504 comes into contact these layers. Therefore, a siliconcarbide (SiC) layer should be provided between the amorphous siliconlayer and the aluminum-made electrode 504. Alternatively, a mixing ofthe aluminum-made electrode 504 with an impurity such as silicon (Si) ora provision of one or two barrier layers using a material other than asilicon carbide (SiC) layer can prevent the corrosion of electrode 504.

A plurality of electrodes may be manufactured in the same productionprocess in a device configuration wherein the electrode 504 has the sameheight as that of one or more electrodes disposed under the end of amirror (not shown in a drawing herein).

As the electrode 504 is deposited in step 2-1, it is preferable toconfirm an absence of abnormality in the operation of a drive circuitand/or the electrical continuity of the electrode 504 by testing thedrive circuit formed on the substrate 501.

Particularly with the electrode 504 formed on the wiring 502 in step201; to the manufacturing process may also form a Via (i.e., anintermediate layer or a connection part) 505 between the wiring 502 andelectrode 504 as shown in step 2-2. The Via 505 is preferably made of anelectrically conductive material such as metals containing tungsten,copper, or aluminum, and to have a horizontal cross-sectional areasmaller than the cross sectional area of electrode 504.

A second protective layer 506 is formed in step 3. The second protectivelayer 506 is deposited on the upper part of the electrode 504 and firstprotective layer 503, also forming a concave opening 506 a in a partwhere the material has flowed into the concave opening 504 a of theelectrode 504. Specifically, the thickness of the second protectivelayer 506 is preferably 500- to 3000 angstroms. Practically, if theprotective film has a thickness of 1000 angstroms or more, the light isabsorbed before reaching inside of the substrate, and thereby theprotective film can reduce the effect of a photoelectric effect on thecircuit inside of the substrate. Blue light is attenuated to about 5% at500 angstroms, while green light is attenuated to about 5% at 1000angstroms. Red light is attenuated to 10% or less at 2000 angstrom.Furthermore, the smaller the gap between mirrors, the more thephotoelectric effect is attenuated because of the illumination lightemitted to the substrate through the gap is reduced.

Furthermore, the amount of reflection light is increased by an increasein the area of the reflection surface of a mirror and thereby a brightimage is produced. The reflection surface of mirrors preferably occupies80% or more (preferably 90% or more) of the area of the mirror array.Moreover, if a mirror comprises a single layer of aluminum, thethickness of aluminum is preferably at least 600 angstrom because theillumination light transmits through an aluminum layer with a thicknessof about 300 angstrom. a. In consideration of a variation in productionand the flatness of the mirror, the thickness of aluminum is preferablyno less than 1500 angstroms, and about 3000 angstroms for a singlelayered structure of aluminum.

Specifically, the second protective layer 506 is accumulated at 380- to400° C. by using silane and argon (SiH4+Ar) in a plasma-enhanced CVD(PECVD) process to form a layer of amorphous silicon as a semiconductormaterial. Note that depositing this layer via a chemical vapordeposition (CVD) process involves deposition of a film utilizing achemical catalytic reaction by supplying a gaseous material inaccordance with the type of the sacrifice layer. The second protectivelayer 506 may be formed as a plurality of layers combined with aprotective layer composed of a material such as silicon carbide (SiC).

In step 4 shown in FIG. 5B, a first sacrifice layer 507 is formed. Thefirst sacrifice layer 507 is deposited at 400° C. by using silane,oxygen, and argon (SiH4+O2+Ar) in high-density plasma (HDP)-PECVDprocess and is formed as a layer of oxide. Note that the top of anelastic hinge (which is described later) is formed with the firstsacrifice layer 507 and therefore the height of the sacrifice layer 507is determined on the basis of a desired height of the elastic hinge asdescribed later.

In step 5, a first photoresist layer 508 is formed by applying a spincoating on the sacrifice layer 507. Then, the holes 506 a and 507 a ofthe first sacrifice layer 507 and second protective layer 506,respectively, are formed in the concave part 504 a of the electrode 504and the upper part surrounding them by applying an etch process to openthe hole.

The hole 507 a is etched in the first sacrifice layer 507 using the gasof octafluorocyclobutane (C₄F₈) and carbon monoxide (CO) by applying areactive ion etching (RIE) process. Furthermore, if the secondprotective layer 506 is made of silicon (Si), the etching is appliedwith hydrogen bromide (HBr) and chlorine (Cl) gas, and, if the secondprotective layer 506 contains silicon carbide (SiC), an etching processis performed by using tetrafluoromethane, oxygen, and argon (CF₄+O₂+Ar)by applying the RIE forms the hole 506 a in the second protective layer506.

In step 6, a second sacrifice layer 509 is deposited in the respectiveholes 506 a and 507 a of the second protective layer 506 and firstsacrifice layer 507, and in the concave part 504 a of the electrode 504.The surface is then planarized by applying a chemical mechanicalpolishing (CMP) process and thereby the step of the upper surfacesbetween the first sacrifice layer 507 and second sacrifice layer 509 isremoved.

In step 7, the second sacrifice layer 509, other than a part 509 athereof is deposited in the surrounding area of the concave part 504 aof the electrode 504, is removed by applying the etching. A secondphotoresist layer 510 is formed in advance of the etching, and then anopening is obtained by the etching.

Note that an elastic hinge (described later) will be extendedperpendicularly upward from the concave part 504 a of the electrode 504along the un-removed part 509 a, of the second sacrifice layer 509.Therefore, the s sacrificial layer 509 a must be formed with aconfiguration in accordance with the size and shape of the elastichinge.

In step 8, shown in FIG. 5C, a hinge layer 511, which will constitute anelastic hinge later, is formed at 380- to 400° C. by using SiH4+Ar byapplying a plasma enhanced chemical vapor deposition (PECVD) process.The thickness of the hinge layer 511 is preferably between 100- and 1000angstroms, in consideration of a spring force for deflecting a mirrorand the electrical resistance of the hinge. The thickness of the hingelayer 511 is no more than 500 angstroms and preferably between 150- and500 angstroms.

Furthermore, a part of the hinge layer 511 includes the surface parallelto a mirror as described below and on which a joinder part 516 a (FIG.5C) is formed is deposited on the upper surface of the first sacrificelayer 507, has a different film thickness in the part perpendicularlydeposited inside the first sacrifice layer 507, with a thicker filmaccumulated toward the upper surface of the first sacrifice layer 507,that is deposited with a thickness two to four times that of the partthat is formed perpendicularly.

The upper part of the first sacrifice layer 507 is preferably thickersince it is a region with little elastic deformation. It also makes itmore convenient to form a joinder part 511 b as will be furtherdescribed below.

The hinge layer 511 may be made from any one or combinations of thefollowing material that includes single crystal silicon, poly-silicon,and amorphous silicon, which is doped with boron (B), arsenic (As), orphosphorous (P) as additive.

Alternatively, the hinge layer 511 may be fabricated with electricalconductivity by applying an in-situ doping with arsenic, phosphorous,and the like, by applying an ion implant or by diffusing a metallicsilicide such as nickel silicide (NiSi) and titanium silicide (TiSi).Furthermore, the hinge layer 511 may be formed with aluminum containingsilicon (Si). Moreover, the hinge layer 511 may be formed with amaterial containing the same material contained in the materialconstituting the first protective layer 503.

Practically, there may be alternative configurations such that theelectrode 504 and hinge layer 511 are fabricated with materials whichcontain the same component material, such that the aforementioned twocomponents are made of the same material, such that the electrode 504has a higher thermal conductivity than that of the hinge layer 511 toconduct heat effectively from the lower part of an elastic hinge asdescribed below. This layer composed of a material different from thematerials of electrode 504 and hinge layer 511 is therefore formedbetween the aforementioned two components.

In step 9, a third photoresist layer 512 is formed on the hinge layer511.

In step 10, the third photoresist layer 512 that covers throughout theupper part of a part of the concave part 504 a of the electrode 504 andthe upper part surrounding the aforementioned part, is removed byapplying etching. The process prepares a space to form a head of anelastic hinge as described below on the lower side. It is followed byetching the hinge layer 511 to form the feature of an elastic hinge. Theetching may use SF₄+O₂+Ar by applying an RIE and isotopic. Furthermore,in step 10, etching is applied such that the width of the elastic hinge(the width is indicated by the width as delineated in the cross-sectionshown in step 10) measures between 0.5- and 1.5 μm on a surface in thedepth direction of the cross-sectional diagram shown in step 10.

In step 11, the third photoresist layer 512 is removed by using O₂, anda third sacrifice layer 513 is formed thereon. Then, the surface issmoothed by applying a CMP planarization process. More specifically, inan exemplary embodiment, the third sacrifice layer 513 may be formed astetraethoxysilane (TEOS) or as a similar layer.

In step 12, shown in FIG. 5D, a fourth photoresist layer 514 is formedon the upper part of an elastic hinge 511 a in order to prepare a spaceto form the head position on the upper side of the elastic hinge 511 a.Then an etching process is applied to remove parts other than theelastic hinge 511 a and the elastic hinge 511 a is formed with thepredetermined height of the third sacrifice layer 513 and hinge layer511. With this process, the elastic hinge 511 a is formed.

The bottom surface of elastic hinge 511 a is attached to the bottomsurface of the concave part 504 a of the electrode 504 and also to thevertical part of the elastic hinge 511 a that extends approximatelyperpendicular to the substrate 501. The elastic hinge is furtherattached to the side surface of the concave part 504 a. Therefore, theelastic hinge 511 a is connected to the electrode 504 inthree-dimensions and fixed securely onto the electrode 504.

Specifically, the elastic hinge 511 a is connected to the electrode 504,which is positioned under the second protective layer 506, so that theelastic hinge 511 a penetrates the second protective layer 506 and stayswithout contact therewith. Furthermore, the elastic hinge 511 a andsecond protective layer 506 are formed not to be electrically conductivewith each other even after the processes of steps as will be describedbelow. Specifically, an insulation layer may be placed between theelastic hinge 511 a and second protective layer 506 so that these twocomponents are not electrically conductive with each other. If thesecond protective layer 506 is made of a high-resistance insulator, theelastic hinge 511 a may be in contact with the second protective layer506.

In step 13, the fourth photoresist layer 514 is removed, and then afourth sacrifice layer 515 is formed. More specifically, the firstthrough fourth sacrifice layers may be formed by using the samematerial. Then, the surface of the fourth sacrifice layer 515 ispolished by applying the CMP planarization process.

In step 14A-1 shows the elastic hinge 511 a supported on the substrate501, which is placed near the center of a wafer Step 14A-2 shows theelastic hinge 511 a at the end of the substrate 501 that is placed atthe end of the wafer. With such configurations, the amounts of polishingare different between the center and surrounding depending on the CMPcondition for the respective wafers. In the step 14A-1, the fourthsacrifice layer 515 can be polished by applying the CMP to the uppersurface of the elastic hinge 511 a. Therefore, a mirror can be formed onthe elastic hinge 511 a. In the step 14A-2, however, the fourthsacrifice layer 515 at the end of the substrate 501 cannot be polishedto the upper surface of the elastic hinge 511 a, creating thepossibility that a mirror (which is described later) cannot be connectedto the elastic hinge 511 a.

Accordingly, an etching process is applied to remove a part of thefourth sacrifice layer 515 positioned on the upper surface of theelastic hinge 511 a. Then a semiconductor material 516 possessingelectric conductivity is formed by applying the CVD as step 14B-1 showsin FIG. 5E. The semiconductor material 516 may use a single crystalsilicon (Si) or poly-silicon. Either of these materials may be dopedwith boron (B), arsenic (As), or phosphorous (P). Furthermore, thesemiconductor material 516 may comprise a material that includes thesame component material as composed in the material for the elastichinge 511 a.

Then, step 14B-2 shows the semiconductor material 516 is removed byapplying etching. One or no less than two joinder parts (i.e., convexpart, conductive part and conductive layer) 516 a are formed in the partfrom which the fourth sacrifice layer 515 has been removed. Then, theupper surfaces of the third and fourth sacrifice layers 513 and 515, andthe upper surface of the joinder part 516 a, are processed throughpolishing by applying the CMP. The joinder part 516 a is set at anecessary height (e.g., 0.1 μm) in accordance with the flatness of thethird and fourth sacrifice layers 513 and 515. Furthermore, the joinderpart 516 a is formed having a size smaller than a mirror 518. Thisconfiguration can prevent a variation of the height of the mirror (518)from the substrate surface that may occur in each region of a wafer orin each wafer.

Furthermore, as a different production method for a joinder part 516 b,a joinder part 511 b can be formed by applying a fifth photoresist layer517 on a part of the upper surface of the elastic hinge 511 a and thenapplying an etching process as shown in step 14C-2, starting from thestate shown in step 14C-1.

Following the steps 14B-1 and 14B-2 after forming the joinder part 516a, In, an aluminum-made mirror (i.e., a reflector mirror) 518 is formedby applying a sputtering process as shown in step 15 of FIG. 5F. Theshape of the mirror 518 may be configured to an approximate square or anapproximate parallelogram in an orthogonal view. Specifically, themirror 518 is formed with the joinder part 516 a projected upward beyondthe sacrifice layers 513 and 515 to join the joinder part 516 a withmirror 518 inside mirror 518.

Then, the first through fourth sacrifice layers 507, 509 a, 513, and 515are removed with a hydrogen fluoride (HF) gas and alcohol as shown instep 16-l in forming the joinder part 516 a, and in step 16-2 formingthe hinge without a joinder part.

If the first through fourth sacrifice layers 507, 509 a, 513, and 515are formed by the TEOS, the first through fourth sacrifice layers areremoved with an HF gas and alcohol. The remaining foreign material andsacrifice layers can be completely removed by adjusting the densities ofthe hydrogen fluoride and alcohol and the processing time. As a result,when the mirror 518 comes in contact with the second protective layer506 on the electrode 504 a stiction between the mirror 518 and thesubstrate can be prevented. Specifically, the first through fourthsacrifice layers 507, 509 a, 513, and 515 may be removed after thesubstrate 501 is cut from its form of a wafer into individual devices byapplying dicing to the wafer. This configuration has the benefits oflaminating a protective layer composed of SiO2 or similar type of layer(not specifically shown in the drawing) to cover and protect the entireupper surface of the mirror 518 before the application of a wafer dicingprocess.

The elastic hinge 511 a and mirror 518 formed on the substrate 501according to above processes is made electrically conductive to a drivecircuit (not shown in a drawing herein) and the electrode 504 forapplying a voltage thereto to deflect the mirror 518.

Furthermore, a light shield layer for suppressing the reflection lightfrom the surface of the protective layer 506 may be formed on thesurface of the protective layer 506. Specifically, the light shieldlayer is preferably a coating layer which would have insignificantinfluence the resistance value of the elastic hinge 511 a.

Meanwhile, there is an anti-stiction countermeasure process forpreventing a moving part (mainly a mirror) from sticking to the stopperthat may be implemented as part of an electrode. The problem of stictionoften causes an operation failure of the mirror devices. Theanti-stiction member may be provided by laminating a monolayer ofperfluorooctyltrichlorosilane (CF₃(CF₂)₅(CH₂)₂SiCl₃; PFOTS),perfluorooctyldimethylchlorosilane (CF₃(CF₂)₅(CH₂)₂Si(CH₃)₂Cl; PFODCS),or perfluorodecyldimethylchlorosilane (CF₃(CF₂)₇(CH₂)₂Si(CH₃)₂Cl;PFDDCS) on the protective layer 506 and mirror 518. When such amonolayer is further deposited on the surface of the protective layer506, it is preferable to use a high resistance material similar to thatof the protective layer 506 to minimize the effects of changing theresistance of the elastic hinge 511 a.

In practice, there are processes for dividing a mirror device by dicingthe wafer into mirror devices of specific predefined size followed bythe packaging processes for enclosing and protecting individual mirrordevices as electronic device packages. A description of these processesis not provided herein.

Practically, it may be preferable to produce the mirror device byconfiguring the elastic hinge 511 a with a height of 2 μm or less, orfurther preferably 0.3 to 1.2 μm, and configuring the mirror 518 of eachmirror element as an approximate square with one side being 10 μm orless.

Furthermore, an elastic hinge connected onto an electrode is placed inthe vicinity of the rear surface of a mirror so that to reduce theillumination light transmitted onto the hinge.

FIG. 6A is a top view diagram showing a mirror element 600; FIG. 6B is aside cross sectional view diagram of the mirror element 600.

The elastic hinge 611 of the mirror element 600 is manufactured by aproduction method by the above-described production method, has theintermediate part 611 m extending in a vertical direction (i.e.,approximately perpendicular to a substrate 601). Furthermore, the upperpart 611 u of the elastic hinge 611 is a flat part extendinghorizontally, bending from the intermediate part 611 m, while the bottompart 611 b of the elastic hinge 611 is a flat part extendinghorizontally, in the direction opposite to the upper part 611 u, bybending from the intermediate part 611 m.

The upper part 611 u of the elastic hinge 611 is connected to a mirror618 interconnected through a joinder part 616. The elastic hinge 611 isplaced at the center of the mirror 618, and the joinder part 616 isplaced at a position with an offset distance away from the center of themirror 618 in the deflection direction thereof. Alternatively, thejoinder part 616 may be placed at a position biased in a directiondifferent from the deflection direction of the mirror 618.

Furthermore, the bottom part 611 b of the elastic hinge 611 is attachedto the bottom surface of the concave part 604 a of an electrode 604,while the intermediate part 611 m is attached to the side surface of theconcave part 604 a.

In FIG. 6A, the joinder part 616 has a rectangular form, with all sidesof the joinder part 616 in the horizontal orientation having aninclination relative to the deflection direction of the mirror 618.Specifically, each side of the joinder part 616 is placed at a 45 degreeangle relative to the deflection direction of the mirror 618. Anirregularity of the joinder part 616 when formed on the reflectionsurface of the top surface of the mirror 618 may cause diffraction lightand/or scattered light in addition to the reflection light whenreflecting the illumination light by the mirror. Even with suchirregularities, the configuration that prevents the irregularity fromcrossing orthogonally with the deflection direction of the mirror canstill minimize the adverse effects caused by diffraction light byminimizing the diffraction light to project together with an ON light.Furthermore, an irregularity on the top surface of the mirror may beminimized by limiting the height of the joinder part 616 to no more than0.1 μm, preferably no more than 0.05 μm. Furthermore, the outer shape ofthe joinder part 616 may be formed with a circle or oval shape having anouter profile that has no straight side.

More specifically, the elastic strength of the elastic hinge for eachmirror element 600 may be greatly affected if the thickness or height ofthe elastic hinge 611 fluctuates in the processes of fabricating theelastic hinge 611. Furthermore, due to the residual stress caused at theproduction, the elastic hinge 611 may be deformed after removing thesacrifice layer surrounding of the elastic hinge 611. Therefore, inorder to manufacture reliable mirror device, the elastic hinge is formedto satisfy the condition that the width of an elastic hinge (i.e., thelength in the depth direction of the cross-section diagram shown in FIG.6B) W>the height L of the elastic hinge

It is desirable that the elastic hinge 611 be placed approximatelyvertical between the center electrode 604 and mirror 618, and to satisfythe relationship of:

the width W of the elastic hinge 611≧the height L of the elastichinge>the thicknesses HP, HU and HL of the elastic hinge

Practically, the inventors of the present invention have experimentaldata to confirm that the mirror 618 deposited on the elastic hinge 611tends to incline instead of maintaining a horizontal position if thecondition of:

the width W of an elastic hinge>the height L of the elastic hinge

is not satisfied in an exemplary embodiment with the height L of anelastic hinge is approximately 1 μm and the width W of the elastic hingeis approximately 0.8 μm.

In contrast, the mirror 618 is stable at a horizontal position when thecondition of:

the width W of an elastic hinge>the height L of the elastic hinge

is satisfied, for an exemplary embodiment with the height L of anelastic hinge 611 is approximately 1 μm and the width W of the elastichinge 611 is approximately 1.2 μm.

Specifically, the width W of each elastic hinge can be reduced when amirror 618 is implemented with multiple elastic hinges 611. However, ifthe elastic hinge has a reduced thickness, it is desirable to satisfythe condition of:

the width W of an elastic hinge>the height L of the elastic hinge

Furthermore, a joinder layer having the same area size and shape as themirror 618, can be deposited on the bottom surface of the mirror 618.For a joinder layer formed with small area, it has an advantage ofavoiding the deformation and/or warping of the mirror 618 due to thedifference in the linear expansion coefficient between the mirror 618and joinder layer.

The intermediate part 611 m of the elastic hinge 611 is tapered off fromthe upper part 611 u toward the bottom part 611 b, with the thicknessgradually decreasing toward the bottom part 611 b (i.e., the thicknessesHU>HL). Specifically, the thickness HP of the upper part 611 u is thesame as that of the uppermost part of the intermediate part 611 m, whilethe thickness of the bottom part 611 b is about the same as that of themiddle part of the intermediate part 611 m.

Furthermore, the elastic hinge 611 preferably satisfies the relationshipof:

the area of a cross-section horizontal to the substrate 601 of the upperpart 611u>the area of a cross-section horizontal to the substrate 601 ofthe bottom part 611b

According to above descriptions, the elastic hinge 611 can be fabricatedwith convenient manufacturing processes. There are further test datawith analytic results to show that the elastic hinges are formed with ahigh durability, so that the elastic hinge is expected to reliablysustain up to several trillion of deflections with malfunctions.

Meanwhile, the height of the electrode 604 from the substrate 601 isapproximately the same as the height of the part of elastic hinge 611that projects from the concave part 604 a of the electrode 604.Alternatively, the height of the projecting part of the elastic hingecan be smaller. This configuration reduces the potential problems suchas having mirror 618 inclined relative to the substrate 601 in theprocess of removing a plurality of sacrifice layers. Furthermore, thesmaller the distance between the mirror 618 and electrode 604, it ismore convenient to make the mirrors with uniform heights on the wafer.

Furthermore, a configuration that makes the height of the elastic hinge611 no more than the distance between the mirror 618 and substrate 601further reduces the potential problems such as having mirror 618 formedwith an inherent inclined angle relative to the substrate 601.

Specifically, FIG. 6B shows a second protective layer 606 is depositedon top of the first protective layer 603. The first protective layer 603is made of a silicon carbide (SiC) material, while the second protectivelayer 606 is made of an amorphous silicon material. The elastic hinge611 is also made of an amorphous silicon material and doped with boron(B), phosphorous (P), or arsenic (As). Because of this, when a voltageis applied to the electrode, the voltage is further applied to themirror 618 through the elastic hinge 611. Alternatively, the mirror 618can be connected to the ground (GND) by way of the elastic hinge 611.Practically, the resistance of the elastic hinge 611 is preferably aresistance value of 1 GΩ or less, or more preferably 100 MΩ or less. Ifthe elastic hinge 611 is made of amorphous silicon, the resistance ishigh and would be approximately 1 TΩ or higher. If the amorphous siliconcontains a very small amount of impurity, the resistance value will beas high as 1000 times. If the resistance value of the elastic hinge 611is high, the electrons would not transmit through the elastic hinge 611smoothly, worsening the response characteristic when the mirror 618deflects. The voltage to be applied to the address electrode for drivingthe mirror 618 may be increased. When the mirror is to be turned On/Offat a high-speed, such as 300 nsec or less, or 100 nsec or less, or even20 nsec or less, the resistance of the elastic hinge is preferably atleast 1 GΩ or less, or further preferably 500 MΩ or less. If the mirrorneeds to be driven at an even higher speed, the resistance value ispreferably 200 MΩ or less, 100 MΩ or less, or even 50 MΩ or less.

On the other hand, the second protective layer 606 is not formed withoutapplying a doping process and therefore remains as a high resistancelayer. Specifically, the resistance value of the second protective layer606 is higher than that of the elastic hinge 611. Furthermore, a mirrordevice is preferably produced with a 0.15- to 0.55 μm gap between themirrors 618 by forming the elastic hinges 611 at the height of 2 μm orless, or more preferably between 0.3- and 1.2 μm, on the electrodes ofapproximately the same heights and by configuring the mirror 618 of eachmirror element as an approximate square with each side being 8- to 10μm. This configuration has a further advantage that the elastic hinge611 is obscurely placed in the vicinity of the rear surface of themirror 618 to reduce the amount of the illumination light directlyilluminated onto the elastic hinge 611. The configuration isadvantageous even if the elastic hinge 611 is made of a semiconductormaterial and has a relatively high resistance value, because themovement of photoelectrons inside the elastic hinge 611 due to theillumination light can be reduced.

FIGS. 7A through 7F are diagrams for describing a mirror element 700.The mirror element 700 shown in FIG. 7A is manufactured by thefabrication processes described above, similar to the fabricationprocesses for the mirror element 600 shown in FIGS. 6A and 6B. Themirror element 700 formed on the substrate 701 includes the wirings 702a, 702 b and 702 c of a drive circuit for driving and controlling amirror 718; first Vias 705 a, 705 b, 705 c, 705 d and 705 e, which areconnected to the wirings 702 a, 702 b and 702 c; and a first insulationlayer 719. Note that the drive circuit may be implemented with thedynamic random access memory (DRAM).

Specifically, the wiring 702 a on the left side of FIG. 7A furthercomprise two of the first Vias 705 c and 705 e, both across the firstinsulation layer 719. The wiring 702 b on the right side of FIG. 7A alsocomprises two of the first Vias 705 b and 705 d, both across the firstinsulation layer 719. Meanwhile, the wiring 702 c at the center compriseone of the first Vias 705 a.

As described above, the first insulation layer 719 is formed with fiveof the first Vias. Practically, the number of first Vias may bedifferent between the left and right wirings. Furthermore, the number offirst Vias may be more, or less, than “5”.

Then, second Vias 720 a, 720 b and 720 c or surface electrodes 721 a and721 b are formed on the first Vias 705 a, 705 b, 705 c, 705 d and 705 e.Specifically, the second Vias 720 a, 720 b, and 720 c are formedrespectively on 1) the first Via 705 a, which has been formed on thewiring 702 s at the center, 2) the first Vias 705 b and 705 c, on oneside, of two first Vias, which have been formed on the wirings 702 b and702 a on the left and right sides. Meanwhile, surface electrodes 721 aand 721 b are formed respectively on the remaining first Vias 507 d and705 e where none of the second Vias 720 a, 720 b, and 720 c is formed.

Then, a first protective layer 703 is formed on the first insulationlayer 719 and a second protective layer 706 is formed on the firstprotective layer 703.

Specifically, the semiconductor wafer substrate 701 may preferably be asilicon substrate.

The wirings 702 a, 702 b, and 702 c of the drive circuit may preferablybe aluminum wirings.

The first Vias 705 a, 705 b, 705 c, 705 d, and 705 e and the second Vias720 a, 720 b, and 720 c may preferably be made of a material includingtungsten and copper.

The surface electrodes 721 a and 721 b may use the same or similarmaterial as tungsten as the first Vias 705 a, 705 b, 705 c, 705 d, and705 e and the second Vias 720 a, 720 b, and 720 c. Alternatively, thesurface electrodes may use a material with high electrical conductivity,such as aluminum. Furthermore, the shapes of the surface electrodes 721a and 721 b may be designed at the producer's discretion. Additionally,the surface electrodes 721 a and 721 b are formed on the first Vias 705d and 705 e, respectively, using the configuration shown in FIG. 7A;alternatively, these electrodes may be formed directly on the wirings702 a and 703 b, respectively.

The first insulation layer 719 and the first and second protectivelayers 703 and 706 may preferably be layers containing silicon such assilicon carbide (SiC), amorphous silicon, and silicon dioxide (SiO2).

If aluminum is used for the surface electrodes 721 a and 721 b, a directcontact between amorphous silicon and the aluminum-made electrode willcause surface corrosions on the aluminum electrodes 721 a and 721 b.Therefore, a silicon carbide (SiC) layer is preferably formed betweenthe amorphous silicon and the aluminum-made surface electrodes 721 a and721 b. Specifically, the electrodes may be formed with alternativeconfigurations such as forming an electrode doped with impurity dopantssuch as silicon (Si), with aluminum, or forming a barrier layer made oftantalum (Ta) or titanium (Ti) on the top or bottom of the electrode.This barrier layer may comprise two or more layers.

Specifically, stiction generated by the contact between the mirror 718and electrodes 722 a or 722 b on the left or right side can also beprevented by forming a stopper on the substrate 701 so that the mirror718 does not come in contact with either electrodes 722 a or 722 b onthe left and right sides.

For the mirror element 700 are formed with electrodes 704, 722 a, and722 b electrically connected to the second Vias 720 a, 720 b, and 720 c,respectively.

The electrodes 704, 722 a, and 722 b may preferably use a material suchas aluminum or similar materials with high electrical conductivity.

The center electrode (i.e., the hinge electrode) 704 is the electrodeformed for an elastic hinge and is configured to have the same height asthe left and right electrodes 722 a and 722 b. A configuration with theindividual electrodes 704, 722 a, and 722 b have the same height on thecenter, left and right sides, these three electrodes 704, 722 a, and 722b may be simultaneously formed in a single processing step.

Furthermore, the center part for placing the elastic hinge 711 may bedetermined by later manufacturing steps by adjusting the height of thecenter electrode 704.

The elastic hinge 711 may be formed by using amorphous silicon. Thethickness (i.e., the left to right direction of FIG. 9A) of the elastichinge 711 may preferably be between about 150- and 400 angstroms.

Specifically, a plurality of elastic hinge with a smaller width may beplaced for one mirror 718. For example, two elastic hinges with asmaller width than an elastic hinge in the configuration of providingone mirror 718 with one elastic hinge may be formed on both ends of themirror.

In an exemplary embodiment, the elastic hinge 711 is formed bydepositing amorphous silicon, poly-silicon, or single crystal silicon byapplying a chemical vapor deposition (CVD) process. It is furtherpreferable to form the elastic hinge 711 with electric conductivematerial by forming the elastic hinges with a silicon material dopedwith a group-III atom such as boron, arsenic, and phosphor or with agroup-V atom. Furthermore, the conductivity of the hinge may be improvedby doping the elastic hinges with two kind of material such as boron andphosphor. The elastic hinge may also be formed by diffusion a metallicsilicide such as nickel silicide (NiSi), titanium silicide (TiSi), etcetera. Additionally, if the mirror 718 and electrode 704 are made ofaluminum, it is desirable to make the elastic hinge electricallyconductive during the production process, which, if conducted at a hightemperature, the aluminum material will migrate to the silicon material.In this case, the electrical resistivity of the elastic hinge 711 isreduced to allow a secure connection of the mirror 718 to the ground(GND). A high resistivity increases the time to generate an electricpotential between the mirror 718 and the electrode 722 a or 722 b thusslowing down the response speed of the mirror. Furthermore, if theelastic hinge 711 is made of a semiconductor material, a photoelectriceffect is generated by the effect of the irradiated incident light,reducing the electric potential between the mirror 718 and the electrode722 a or 722 b with time and making it very difficult to retain themirror 718 on the electrode (722 a or 722 b).

Due to the above-described technical concerns, the resistivity of theelastic hinge 711 is should be no higher than 1 giga-ohms. The elastichinge may have a preferable resistivity not higher than 0.5 giga-ohms,depending on the usage environment. A further reduction of resistivityto 0.2 giga-ohms makes it possible to provide a video image with a highgrade of gradation as a result of enabling the mirrors to operate at ahigh speed. Furthermore, if the elastic hinge 711 is made of silicon andthe like, more benefit can be realized because the electrical resistanceis reduced with temperature.

Furthermore, if the elastic hinge 711 is made of a silicon material, themechanical property of the elastic hinge 711 would have insignificantchanges with an increase of the environmental temperature to a pointwhere the withstanding temperature of the deflective mirror device is ashigh as the thermal property of a transistor. Therefore, if theconventional environmental temperature is around 40° C. to 45° C., itcan be raised to around 50° C. to 85° C. A display apparatus may beimplemented with a brighter illumination without requiring a coolingdevice and without requiring an apparatus to have greater size due to aheat dissipation requirement. The configuration enables the manufacturerto keep the overall system compact.

If the material of the elastic hinge 711 is amorphous silicon withoutimpurity dopant, the resistance of the elastic hinge is two three ordershigher compared with the doped hinges. With such high resistance, themirror 718 is electrically floating. Therefore, even a high voltageapplied to the electrode 116 may not generate different electricalpotentials immediately between the mirror and electrode 116. Even thougha high voltage continuously applied to the electrodes may generatecertain level of potential difference, the operation requires a longperiod of time. The mirror device thus prevents a high speed modulatingoperation. Moreover, when the illumination light is irradiated on theelastic hinge 711, the influence of a photoelectric effect causes acurrent to flow to the mirror 718 by way of the elastic hinge 711. Thisin turn causes a gradual reduction in the difference in potentials inthe state of the mirror 718 being deflected to the direction of eitherelectrode 722 (i.e., 722 a or 722 b), making it impossible to retain themirror 718 to either electrode. If the elastic hinge 711 is made ofaluminum or a similar material, the electric resistance is very small.There is, however, deterioration due to metallic fatigue, et cetera,making for inferior durability. Therefore, the use of a material that issuperior in mechanical strength, such as silicon, with a lower electricresistance, has an advantage as a display device durable in high speedoperation for an extended length of time.

Specifically, when the elastic hinge 711 is made of a silicon materialwith an electric resistance of 2 about giga-ohms, the irradiation withlight for an extended length of time gradually decreases the potentialbetween mirrors retained onto the electrode and eventually releases theretention of the mirror to return to a horizontal state. Setting up thequantity of illumination light and the resistance value of the elastichinge at respective predetermined values makes it possible to set thetime period of retaining the mirror using the light. Alternatively, theCoulomb force generated between the mirror and electrode can be reducedwith time. This also makes it possible to alleviate the effect ofstiction, a phenomenon in which a mirror retained onto an electrode isstuck to the electrode. Furthermore, the desired operation of the mirrorcan be controlled with the light. Additionally, for the mirror element700, a second insulation layer (i.e., a protective film) 723 is formedon the surface of the structure part of the substrate 701. Specifically,the second insulation layer 723 and center electrode 704 are connectedto a GND potential.

The second insulation layer 723 may preferably be a layer containingsilicon (Si), such as silicon carbide (SiC) and amorphous silicon forpreventing corrosion caused by hydrogen fluoride (HF). Particularly,when the electrodes 704, 722 a, and 722 b and surface electrodes 721 aand 721 b are formed as aluminum electrodes.

Furthermore, the top surface of the elastic hinge 711 may furtherinclude a joinder layer. A layer made of the same material to form theelastic hinge may be used as the joinder layer by configuring it to havethe same area size and form as the mirror 718. The configuration of thejoinder layer may be formed to have the smallest possible area toprevent the mirror 718 from deforming and/or warping due to thedifference in linear expansion coefficient between the mirror 718 andthe joinder layer.

Furthermore, a joinder layer (i.e., mirror connection part) 716 isformed on the joinder layer of the elastic hinge 711 for providing anelectric conduction between the elastic hinge 711 and mirror 718 whileeliminating a variation in the height among the individual mirrorelements.

The joinder layer 716 may preferably be made of, for example, singlecrystal silicon (Si), amorphous silicon, or poly-silicon, all of whichis applied with an In-Situ doping with boron, arsenic, or phosphorous,or an ion-implanted material or an annealed semiconductor material.Alternatively, the joinder layer 716 may preferably have electricalconductivity by using a diffusing a metallic silicide such as nickelsilicide (NiSi) and titanium silicide (TiSi). If the joinder layer 716is made of silicon (Si), as an element in the IV group amongsemiconductor materials, an additive may be appropriately selected fromamong the materials belonging to the III group or V group.

The resistance of the joinder layer 716 may be approximately the same asthat of the elastic hinge 711 or mirror 718, and is lower than theresistance of the first and second protective layers 703 and 706.

If the mirror 718 is made of aluminum and if the elastic hinge 711 isformed by using a silicon material, a barrier layer (not shown in adrawing herein) may be deposited on the top and bottom surfaces of thejoinder layer 716 to prevent the mirror 718 to contact with the elastichinge 711. Such a barrier layer may be formed to have two or morelayers.

Then, the mirror 718 is formed on the joinder layer 716 of the elastichinge 711 to complete the manufacturing processes of the mirror element700.

The mirror 718 may be made of a member possessing a high reflectance oflight, e.g., aluminum. Furthermore, the aluminum used may be an alloycontaining titanium (Ti) and/or silicon (Si). Meanwhile, the top surfaceof the mirror 718 may be provided with an aluminum oxide layer.

Additionally, the mirror 718 may preferably be a square or a diamondshape, with each side having a length about 4- to 11 μm. Furthermore,the gap between individual mirrors 718 may preferably be about 0.15- to0.55 μm. In addition, an opening ratio of an individual mirror element(i.e., the ratio of the area size occupied by the mirror 718 (i.e., areflection region) to the area size consisting of the mirror 718 maypreferably be designed and arranged in an array and the gap betweenmirrors 718) is no less than 85%, or more preferably, no less than 90%.Even in the case of the elastic hinge 711 that is made of asemiconductor material and having a relatively high resistance value, aninfluence such as the movement of photoelectrons inside the elastichinge 711 due to the illumination light can be reduced. Specifically,the reflection region may preferably occupy about 85% of the region inthis configuration for placing the mirrors 718, even when a torsionhinge is used.

FIG. 7B shows the surface part of the substrate 701 that includes themirror 718, the left and right electrodes 722 a and 722 b, and thecenter electrode 704 enclosed by the dotted lines. The deflection axis718 a of the mirror 718 is indicated by a single-dot chain line.

As shown in FIG. 7B, the surface electrodes 721 a and 721 b have theappearance of a rectangle in the plain view, and are placed under theopposite corners of the mirror 718. Furthermore, the surface electrodes721 a and 721 b are symmetrically placed about the center of the mirror718. Specifically, the surface electrode 721 may be provided by arrayinga plurality of miniature electrodes as indicated by the component signs721 c and 721 d shown in FIG. 7C. The individual miniature electrodesare connected to Vias 705 and maintained at the same potential. Theindividual miniature electrodes can be simultaneously manufactured bythe same production process as that for forming a Via connecting betweenmetallic layers in the semiconductor production process, and thusproduction is easily carried out.

The electrodes 722 a and 722 b positioned on the left and right sides ofthe elastic hinge 711 are placed at positions except for the surfaceelectrodes 721 a and 721 b, and hinge electrode 704 under the mirror718. Alternatively, the electrodes 722 a and 722 b may also be placed byoverlapping in entirety, or in part, with the surface electrodes 721 dand 721 e as delineated in FIG. 7C. If the voltages applied to thesurface electrodes 721 and electrodes 722 are applied at the same timeor with the same potential, the surface electrodes 721 and electrodes722 may be electrically conductive to each other. In contrast, if thevoltages are applied to the surface electrodes 721 and electrodes 722 indifferent timings or with different voltages, then different drivecircuits may be connected to the respective electrodes 721 andelectrodes 722 by forming these electrodes without electric connections.

Then, the electrodes 722 a and 722 b are also symmetrically placedrelative to the center of the mirror 718, likewise the case of thesurface electrodes 721 a and 721 b.

FIG. 7D is a top view diagram of the mirror element 700 excluding themirror 718 with the mirror 718 is delineated by a dotted line box.

As shown in FIGS. 7A and 7D, the electrodes 722 a and 722 b are formedto project from the substrate 701. Then, the electrodes 722 a and 722 bare formed to contact the mirror 718 when the mirror 718 deflects to amaximum deflection angle.

The electrodes 722 a and 722 b may be formed to define the deflectionangle of the mirror 718 between 12- and 14 degrees. The deflection angleof the mirror 718 may preferably be designed in compliance with thedesigns of the light source and optical system of a projectionapparatus. A preferable design may also include predefined height of theelastic hinge 711 of each mirror element 700 to be no larger than 2 μmand the mirror 718 of each mirror element 700 to be a square with eachside being no larger than 10 μm.

The ON state of a mirror element 700 is illustrated in FIG. 7E, wherethe mirror 718 reflects the incident light emitted from a light sourcealong a direction to function as the ON light when the mirror 718deflects to the right side.

In contrast, the OFF state of a mirror element 700 is illustrated inFIG. 7F, where the mirror 718 reflects the incident light emitted from alight source along a direction to function as the OFF light when themirror 718 deflects to the left side.

When no voltage is applied to surface electrodes 721 a and 721 b on theleft and right sides of the mirror element 700 and electrodes 722 a and722 b, the elastic hinge 711 is released to a natural state, and themirror 718 accordingly is controlled to maintain in a horizontaldirection.

Specifically, when a voltage is applied to the electrode 722 b andsurface electrode 721 a, both on the right side, a Coulomb force isgenerated between the mirror 718 and the electrode 722 b on the rightside (and the surface electrode 721 a on the right side) as thatdetermined by the following expression:

(the upper surface area of an electrode)×(the applied voltage to anelectrode)/(the second power of the distance between the electrode andmirror)

Then, the mirror 718 is drawn by the Coulomb forces and deflected to theright side.

Specifically, the distance between the mirror 718 and the right-sidesurface electrode 721 a is larger than the distance between the mirror718 and the right-side electrode 722 b and so is the surface area.Therefore the Coulomb force generated between the mirror 718 and theright-side surface electrode 721 a is smaller than that generatedbetween the mirror 718 and the right-side surface electrode 721 a.

Furthermore, when the mirror 718 is deflected to approach the right-sidesurface electrode 721 a, the reaction force is now strong due to therestoring force of the elastic hinge 711 as a result of the mirror 718is deflected to 12- to 14 degrees. The right-side surface electrode 721a placed on the surface of the substrate, however, is capable of drawingthe mirror 718 with a smaller Coulomb force by taking advantage of theprinciple of the lever (i.e., the principle of movements of a rigidbody), that is, by directing the Coulomb force to attract the right endpart, that is, a long distance from the elastic hinge 711, of the mirror718. As a result, the right-side surface electrode 721 a is capable ofretaining the deflection of the mirror 718 in the state in which a lowvoltage is applied.

When the mirror 718 is deflected to the right side as described above,the reverse-side (i.e., the left side) surface electrode 721 a and theleft-side electrode 722 a are maintained at the same potential andgrounded by being connected to the GND.

Specifically, the elastic hinge 711 has the largest elastic stress atthe bottom part on the side of the electrode 704 in a deflected state.

When the mirror 718 is deflected to the reverse side as the mirrorelement 700 is in the OFF light state as shown in FIG. 7F, a voltage isapplied to the electrode 722 a and surface electrode 721 b on theopposite side to change and control the mirror 718 to operate in the ONlight state.

Specifically, when the shapes of the mirror 718 and elastic hinge 711are changed, or when the elastic hinge 711 is made with materials thathas a different restoring force, or when the deflection control for themirror 718 is changed, between the left and right sides of the mirrorelement 700, a voltage may be applied. Adjustments of mirror control foroperating the mirror 718 may be achieved by changing the area size,height and/or placement (i.e., the layout) of the respective surfaceelectrodes 721 a and 721 b or electrodes, 722 a, 722 b, and 704 betweenthe right and left sides of the mirror element 700.

Moreover, application of multi-step voltages to the surface electrodes721 a and 721 b and respective electrodes 722 a and 722 b on the rightand left sides of the mirror element 700 may also be performed tocontrol the mirror operations.

Furthermore, the circuit configurations and different level of voltagesfor driving the surface electrode or electrode of either one of theright-side surface electrodes 721 a and electrode 722 b and theleft-side surface electrodes 721 b and electrode 722 a of the mirrorelement 700 may be appropriately adjusted.

Furthermore, at least one surface electrode of the right-side surfaceelectrode 721 a and left-side surface electrode 721 b of the mirrorelement 700 may be formed with protrusions from the substrate.

Next is a description of the circuit configuration of the mirror element700 with reference to FIG. 7G.

FIG. 7G is a functional block diagram showing an exemplary configurationof a circuit for the mirror element 700 shown in the above describedFIG. 7A. The mirror element array of the mirror device 200 used for theindividual embodiment arranges, in grid-like fashion, a plurality ofmirror elements 700 at the respective position. The bit lines 190 (i.e.,a first bit line 191 and a second bit line 192) vertically extend from abit line driver (not shown in the drawing) and cross a word line 193horizontally extend from a word line driver (not shown in the drawing).

An OFF capacitor 195 b is connected to the electrodes 722 a and 721 b onthe OFF side, and the OFF capacitor 195 b is connected to the first bitline 191 interconnected by a gate transistor 195 a that includes a fieldeffect transistor (FET) or similar circuits.

An ON capacitor 196 b is connected to the electrodes 722 b and 721 a onthe left side designate as an ON direction, and the ON capacitor 196 bis connected to the second bit line 192 by way of a gate transistor 196a that further includes a field effect transistor (FET) or similarcircuits.

The OFF capacitor 195 b and gate transistor 195 a of the electrodes 722a and 721 b on the OFF side comprises a memory cell M1 commonly known asthe DRAM structure. Likewise, the ON capacitor 196 b and gate transistor196 a of the electrodes 722 b and 721 a on the left side along an ONdirection comprises a memory cell M2 in a commonly known DRAM structure.

The elastic hinge 711 supporting the mirror 718 is drawn as a circuitelement having a hinge resistance R711. Furthermore, if the floatingcapacitance of the elastic hinge 711 is large, the circuit may include acapacitor (not shown in a drawing). One end of the elastic hinge 711 isconnected to a grounding unit illustrated as a GND electrode.

In this circuit configuration, both the mirror 718 coupled to theelectrodes (i.e., the electrodes 722 b and 721 a) on the ON side, andthe mirror 718 coupled to the electrodes (i.e., the electrodes 722 a and721 b) constitute as a variable-capacitance capacitor. Therefore, thedeflecting operation of the mirror 718 is controlled by the differencein potentials of the variable-capacitance capacitor. The application ofa voltage to the electrodes 722 a and 721 b on the OFF side, and to theelectrodes 722 b and 721 a, are controlled by the existence or absenceof data written to the respective memory cells M2 and M1. Furthermore,the operations of charging or discharging a charge to or from thecorresponding capacitors control the writing of the data to respectivememory cells.

More specifically, a discretionary word line 193 is selected by a wordline driver, and the switching ON/OFF of the gate transistors 195 a and196 a of the mirror elements 700 on the horizontal one row lining up onthe selected word line 193 is controlled. In association with thisoperation, the bit line driver controls charging and discharging to andfrom the OFF capacitor 195 b and ON capacitor 196 b by way of the firstand second bit lines 191 and 192.

Accordingly, a voltage is then applied to the electrodes 722 a and 721 bon the OFF side and to the electrodes 722 b and 721 a on the ON side,and thereby controlling the deflecting operation of the mirror 718.

Specifically, when a voltage is applied to the electrodes (i.e., theelectrodes 721 b and 722 a, or the electrodes 721 a and 722 b), thecharge of the opposite mirror 718 instantly flows to the ground (GND) ifthe resistance of the elastic hinge 711 (i.e., the hinge resistance711R) is small. If the resistance of the elastic hinge 711 is large, thechange generated in the opposite mirror 718 takes time to flow to theground (GND). This causes the mirror 718 to tilt and generate atransient property, thus generating a delay in the deflecting control ofthe mirror 718.

Furthermore, if the resistance of the elastic hinge 711 is high, and ifthere is an influence of a photoelectric effect due to the illuminationlight by mirror 718 being retained onto the electrodes 722 a and 721 bon the OFF side or onto the electrodes 722 b and 721 a on the ON side,the potential of the mirror 718 is not retained at a constant. Instead,the potential is decreased with the passage of a certain period of time.Therefore, the mirror 718 can no longer be retained by the electrode tomaintain on the OFF side or ON side, as described above.

Furthermore, if the resistance of the elastic hinge 711 is high and ifthe voltage applied to the electrode on the OFF side or ON side issteep, the alternate current (AC) component is actually applied to themirror 718 through the variable-capacity capacitor interconnectedbetween the mirror 718 and each respective electrode (either on the OFFside or ON side). If the potential of the electrode is turned from 5 to0 volts when the mirror 718 is in contact with the electrode on the OFFor ON side, a voltage anywhere between −4 volts and −5 volts is appliedto the mirror 718. Under such circumstance, the mirror 718 remains at aposition retained onto the electrode for a while because of the voltageapplied to the mirror 718, even if the mirror 718 is resists retentionon the electrode. In order to prevent such a condition from occurring, astopper specifically for defining a maximum deflection angle of themirror 718 is connected to the ground (GND). Therefore, the mirrorelement 700 can be controlled to operate at a high speeds with highreliability.

FIG. 7H is a circuit diagram showing an exemplary modification of theabove described FIG. 7G. FIG. 7H illustrates the elastic hinge 711connected to a hinge line 181 in instead of the fixed potential (GND).

FIG. 7I is a circuit diagram showing the equivalent circuit of theconfiguration of the mirror element 700 as that illustrated in theabove-described FIG. 7G In the configuration of FIG. 7I, the hingepotential V711 of the hinge line 181 is applied to the ground sidedisposed on the other side of a hinge resistance R711, e.g., aresistance of approximately 1 giga-ohm, which is equivalent to theresistance of the hinge from the mirror 718.

Furthermore, the electrode 721 b and mirror 718 form a parasiticcapacitor Q721 b, e.g., a capacitor having a capacitance of 1.5 femtofarads (fF), while the electrode 722 a and mirror 718 form a parasiticcapacitor Q722 a, e.g., a capacitor having a capacitance of about 3 fF),with an OFF-side electrode potential VM1 applied to these capacitors.

Likewise, the electrode 722 b and mirror 718 form a parasitic capacitorQ722 b, e.g., a capacitor with a capacitance of about 0.15 fF, while thesurface electrode 721 a and mirror 718 form a parasitic capacitor Q721a, e.g., a capacitor having a capacitance of about 0.075 fF, with anON-side electrode potential VM2 applied to these capacitors.

Specifically, the capacitance of each capacitor illustrated in FIG. 7Iindicates the capacitance when the mirror 718 is deflected to the OFFside and, therefore, the capacitance is symmetrically changed overbetween the ON and OFF states when the mirror 718 is deflected to the ONside.

When the pixels of a high definition image (e.g., a full high definition(full-HD)) are expressed in 10 bits, the time constant of an RC circuitis functionally related to the hinge resistance R (i.e., the hingeresistance R711), mirror 718, and capacitor C (i.e., parasiticcapacitors Q721 b, Q722 a, Q722 b and Q721 a). The electrodes may beapplied with voltages to modulate with a period equal to or smaller than40 microseconds (μsec) for driving all the ROW lines. Since thecapacitance of the capacitor is inherently determined by the size of apixel and the size of the electrode driving the pixel, the hingeresistance R711 of the elastic hinge 711 is basically limited to a rangeof about one giga ohms or lower when the elastic hinge 711 is made ofpoly-silicon.

An elastic hinge 711, e.g., a hinge that is 0.6 μm long, 1.2 μm wide and250 angstroms thick, manufactured by using amorphous silicon (Si) withan n-type or p-type atomic doping may have a resistance approximately0.1 giga-ohms or higher.

The mirror 718 is in contact with the electrode (i.e., the electrode 722b or 722 a) through the insulation film. Depending on the kind ofinsulation film, the resistance of the electric path through the mirror718 and electrode with the insulation film intervening in between, mayhave a resistance having a range less than 1 giga-ohms.

FIG. 7J is a timing diagram illustrating the relationship between thetiming of applying a hinge potential from a hinge line and thedeflecting operation of a mirror according to the preferred embodiment.

Specifically the mirror displacement profile 110 indicates thedeflection state of the mirror 718 if elastic hinge 711 consists ofpoly-silicon, while the mirror displacement profile 120 indicates thedeflection state of the mirror 718 if elastic hinge 711 is formed byusing of amorphous silicon (Si) doped with an n-type or p-type dopantions.

When the ON-side electrode potential VM2 applied to the electrodes(i.e., 721 a and 722 b) on the ON side when the mirror 718 is tilted tothe ON side and changed from V1 (e.g., 10 volts) to 0 volts, thepotential of the mirror 718 (i.e., a mirror potential V718) firstincreases to a potential close to a-V1 (i.e., a peak potential V718 a),followed by gradually decreasing to 0 volts, because the hingeresistance R711 of the elastic hinge 711 is high.

More specifically, as illustrated in the mirror displacement profile 111on the left side of the mirror displacement profile 110, even when theON-side electrode potential VM2 of the electrodes (i.e., 721 a and 722b) on the ON side are decreased to L (i.e., 0 volts), a large Coulombforce is generated between the mirror 718 and electrode on the ON side.The mirror 718 continues to stay at the ON side (for a period a) even ifthe OFF-side electrode potential VM1 is turned to V1 (volts). This issimilar to the case of mirror displacement profile 120.

Thereafter, when the potential of the mirror 718 decreases, it isdeflected to deflect to the OFF side.

Then, when the electrodes (i.e., 721 a and 722 b) on the ON side aredecreased from V1 to 0 volts, and also the electrodes (i.e., 721 b and722 a) of the OFF side are increased from 0 volts to V1, the mirror 718tilts to the ON side. The hinge potential V711 of the hinge line 181connected to the elastic hinge 711 is set at V1, i.e., the hingepotential pulse V711 a, for a pulse width t2, e.g., 1 μsec which is thetiming b shown in FIG. 7J. The voltage then decreases from the peakpotential V718 b in the mirror 718, causing the mirror 718 to shiftimmediately (i.e., without a delay of the period a) toward theelectrodes on the OFF side as indicated by the mirror displacementprofile 112.

With this operation, the time period for the mirror is controlled tostationary stay at the ON side is reduced to a mirror ON period t3(e.g., 35 μsec) that is shorter than the mirror ON period t1 (e.g., 40μsec) on the ON-side electrode.

As described above, the controlling of the hinge potential V711 appliedto the elastic hinge 711 from the hinge line 181 can speed up theoperation of the mirror element 700 by controlling the hinge potentialV711 at a discretionary timing, thereby attaining a high level ofgradation.

With the configuration and control process, the hinge potential pulseV711 a of the hinge potential V711 may be controlled to have a stepwisewaveform or ramp waveform instead of the pulse waveform shown in FIG.7J.

The following is a description of different mirror behavior depending onthe material of the elastic hinge 711, in the present embodiment. Thehinge potential pulse V711 a is turned to H (high) at the timing capplied to the hinge line 181. The hinge line 181 is connected to theelastic hinge 711. Then, the ON-side electrode potential VM2 of theelectrodes 721 a and 722 b on the ON side is turned from V1 to zerovolts when the mirror 718 is deflected to the ON side. Meanwhile, theOFF-side electrode potential VM1 of the electrodes 721 b and 722 a onthe OFF side is maintained at 0 volts.

With elastic hinge 711 made of poly-silicon, the mirror 718 shifts toand stays at the horizontal position without oscillating, as indicatedby the mirror displacement profile 113.

In contrast, with the elastic hinge 711 is made of amorphous siliconwith an n-type or p-type or p- and n-type impurity dopant ions, themirror 718 oscillates between the ON and OFF positions as indicated bythe mirror displacement profile 123 of the mirror displacement profile120.

Specifically the mirror displacement profiles 121 and 122 of the mirrordisplacement profile 120 are similar to the mirror displacement profiles111 and 112 of the mirror displacement profile 110.

FIG. 7K is a timing diagram showing the polarity of the drive voltagefor a mirror that is reverse from that shown in FIG. 7J.

Specifically, if the change in potentials of the electrode close to themirror 718 is positive, as shown in the above described FIG. 7J, thechange in potentials of the hinge potential V711 applied to the elastichinge 711 from the hinge line 181 is also positive. If the change inpotentials of the electrode close to the mirror 718 is negative, achange in potentials (i.e., the hinge potential pulse V711 b) of thehinge potential V711 is applied to the elastic hinge 711. The deflectionof the mirror 718 is controlled to operate as that shown in FIG. 7K.

When the pixels of the full HD are displayed in 10 bits, it is necessaryto drive all ROM lines within 40 μsec, and perform the respectivetransitions in a sufficiently short amount of time (i.e., within 10μsec) between the above described stationary states in the ON,horizontal, and OFF states.

FIG. 7L is a timing diagram for showing an exemplary modification of thedeflection control for the mirror illustrated in the above describedFIG. 7J.

Specifically FIG. 7L illustrates a voltage as a hinge potential pulseV711 c applied to the hinge line 181 is increased to V2 (e.g., 15 volts)and pulse width t4 (e.g., 3 μsec), which are V1 (e.g., 10 volts) andpulse width t2 (e.g., 1 μsec) in the configuration of the abovedescribed FIG. 7J.

FIG. 7L shows the control process with the potential of the mirror 718fluctuates between both positive and negative. Specifically, if a hingepotential pulse V711 c, with a relatively large V2, is adjusted to thehinge potential V711, the mirror 718 comes apart from the electrode whenthe peak potential 718 c of the mirror 718 is lower than the mirrorholding voltage Vh for retaining the mirror 718 that is close to timingd of the hinge potential pulse V711 c. Then a “brake” is applied to theoscillation of the mirror 718 when a peak potential V718 d exceeds themirror hold potential Vh once again on the opposite side.

Under this circumstance, if the elastic hinge 711 is made of relativelylow resistance doped silicon and the peak potential V718 a of the mirror718 is relatively low, the mirror 718 performs an intermediateoscillation, as indicated by the mirror displacement profile 123 a, at asmaller rather than a full amplitude oscillation in accordance with themirror displacement profile 123 (refer to FIG. 7J).

In contrast, if the elastic hinge 711 is made of relatively highresistance silicon without doping and the peak potential V718 a of themirror 718 is relatively high, the mirror 718 becomes stationary in thehorizontal state as indicated by the mirror displacement profile 113.

FIG. 7M is a circuit diagram showing an exemplary modification of thecircuit configuration as that illustrated in FIG. 7G.

FIG. 7M shows a circuit comprises a plurality of first plate lines 194 band second plate lines 194 a. Specifically, the electrodes 721 a and 721b are separated from the memory cells M2 and M1, respectively, and thememory cells M2 and M1 are independently connected to the plurality offirst and second plate lines 194 b and 194 a. The circuit configurationis different from the above described FIG. 7G.

FIG. 7N is a circuit diagram showing an equivalent circuit with a mirrorcontrolled to operate in an OFF side with the circuit configurationillustrated in FIG. 7M.

FIG. 7N illustrates a circuit with the hinge resistance R711 (e.g., 1giga-ohms) grounded, and the parasitic capacitor Q721 b (e.g., 1.5 fF),parasitic capacitor Q722 a (e.g., 3 fF), parasitic capacitor Q722 b(e.g., 0.15 fF), and parasitic capacitor Q721 a (e.g., 0.075 fF) drivenby the first plate line potential V194 b, OFF-side electrode potentialVM1, ON-side electrode potential VM2, and second plate line potentialV194 a, respectively.

FIG. 7O is a timing diagram for showing an exemplary functional controlprocess with the circuit configuration illustrated in FIGS. 7M and 7N.

Specifically, FIG. 7O shows the control processes of the mirror 718 whena first plate line potential V194 b and second plate line potential V194a are controlled to operate with pluralities of the first plate lines194 b and of the second plate lines 194 a, respectively.

In a state in which no voltages are applied to the first plate line 194b and second plate line 194 a, the peak potential V718 a of the mirrorpotential V718 induced in the mirror 718 by the electrode 722 a (or 722b) gradually decreases from the state of exceeding the mirror holdpotential Vh. Therefore, a delay is generated in the transition from theON state to OFF state by a time period a (e.g., 5 μsec) as indicated bythe mirror displacement profile 131 of the mirror displacement profile130. Consequently, a mirror ON period t11 (e.g., 40 μsec) shiftsbackwards. Because of this, a mirror OFF period t13 (e.g., 35 μsec)between an ON state and the next ON state becomes shorter than themirror ON period t11.

In contrast, by applying a pulse potential VP1 and a pulse potential VP2to the first plate line 194 b (i.e., the electrode 721 b) and secondplate line 194 a (i.e., the electrode 721 a) with a pulse width t12(e.g., 10 μsec) at the time starting the transition between the ON stateand OFF state of the mirror 718, causes the peak potential V718 e of themirror potential V718 is lower than the mirror hold potential Vh. As aresult, the deflecting operation of the mirror 718 can be controlled torespond to the change of the ON-side electrode potentials VM2 andOFF-side electrode potentials VM1 without delay as indicated by themirror displacement profile 132. The width of the ON period is the sameas the mirror ON period t11 by synchronizing with the change ofpotentials of the electrode 722 a

Meanwhile, if a pulse potential VP2 is applied only to the second plateline 194 a at the time of changing from the OFF state to ON state, themirror is controlled to operate according a waveform (i.e., the mirrorON period t14 (e.g., 45 μsec)) with the ON period widened by the period“a”, as indicated by the mirror displacement profile 131.

As described above, the mirror 718 responds quickly to the change involtage of the address electrode (i.e., the electrode 722 a or 722 b) byapplying the first plate line potential V194 b and second plate linepotential V194 a to the electrode 721 b and electrode 721 a.Furthermore, the ON periods of the mirror 718 may be changed bygenerating a voltage only on one side of the first plate line 194 b andsecond plate line 194 a.

Specifically, in the exemplary modification shown in FIG. 7M, change theON/OFF operations of the mirror 718 may be achieved by controlling ofthe potentials of the first plate line 194 b and second plate line 194a, thereby attaining a higher level of gradation for image display.

As described above, if the electric resistance of the elastic hinge 711(i.e., the hinge resistance R711) is high, and if a steep potential isapplied to an electrode on the OFF side or ON side (i.e., an OFF-sideelectrode potential VM1 or ON-side electrode potential VM2), an ACcomponent is actually applied to the mirror 718 through a variablecapacitance capacitor (i.e., the parasitic capacitors Q721 b, Q722 a,Q722 b and Q721 a) between the mirror 718 and individual electrodes.

In order to prevent such a situation from occurring, a voltage isapplied to the first plate line 194 b and second plate line 194 a in adirection to cancel the difference in potentials between the mirror 718and electrode as illustrated in FIG. 7O. The mirror 718 can therefore becontrolled to operate at a high speed or at a discretionary timing. Ahigh level of gradation may be attained by applying such a controlprocess to a single-side electrode. Such a voltage applied in adirection of the cancellation may use a pulse waveform, a stepwisewaveform, or a ramp waveform.

FIG. 7P is a diagram for showing the temperature characteristic of theelectrical resistance of a material constituting an elastic hingeaccording to the present embodiment.

Specifically, FIG. 7P shows that the elastic hinge 711 according to thepresent embodiment has a negative resistance-temperature characteristic.The resistance (i.e., a hinge resistance R711) decreases with anincrease of the temperature of the elastic hinge 711.

In an exemplary embodiment according to FIG. 7P, the hinge may have aresistance of 2 giga-ohms at the ambient temperature (20° C.), whereasit is reduced to 0.5 giga-ohms at 50° C., which is the operatingtemperature of the mirror element 700.

With such hinge, the hinge resistance R711 of the elastic hinge 711 hasa negative temperature characteristic shortens the time (i.e., theperiod a) for the peak potential 718 c of the mirror potential V718 ofthe mirror 718 that is supported by the elastic hinge 711 decreasing tothe mirror hold potential Vh or lower, thereby making it possible toimprove the responsiveness (i.e., the follow-up capability) to thedeflecting operation of the mirror 718 against the ON-side electrodepotential VM2 and OFF-side electrode potential VM1.

FIG. 7Q is a diagram for showing an exemplary method for displaying animage with gray scales utilizing a horizontal stationary state of amirror in addition to an operation for deflecting it to ON/OFF states.

FIG. 7Q illustrates a mirror displacement profile 141, a mirrordisplacement profile 142, a mirror displacement profile 143, and amirror displacement profile 144, as mirror displacement profile 140.

The mirror displacement profile 141 is an example of attaining a 100/100gray scale, i.e., a gray scale with 100% of the maximum brightness, byincluding a horizontal stationary period 141 a in a latter part of theON deflection period 141 b.

The mirror displacement profile 142 is an example of attaining a 50/100gray scale, i.e., a gray scale with 50% of the maximum brightness, byincluding a horizontal stationary period 142 a in a latter part of theON deflection period 142 b.

The mirror displacement profile 143 is an example of attaining a 25/100gray scale, i.e., a gray scale with 25% of the maximum brightness, byincluding a horizontal stationary period 143 a in a latter part of theON deflection period 143 b.

The mirror displacement profile 144 is an example in which no ON periodexists in the periods of individual sub-frames 101 and a 1/100 grayscale, i.e., a gray scale with 1% of the maximum brightness, is attainedby including a horizontal stationary period 144 a only in the initialsub-frame 101.

Gradation is changed by changing the length for ON and intermediateperiods of the mirror 718, as indicated by the above described mirrordisplacement profile 140. Specifically, the OFF, ON, intermediate, andOFF states of the mirror 718 are repeated in the aforementioned order inthe example of FIG. 7Q. The minimum gray scale change is controlled bychanging the length of the horizontal stationary period 144 a of themirror displacement profile 144.

According to such control process, various gray scales can be achievedby combining the above described mirror displacement profiles 141through 144.

Specifically the horizontal stationary periods 141 a, 142 a, 143 a, and144 a can be controlled by the hinge line 181 controlling the hingepotential V711, i.e., by controlling the mirror potential V718, asindicated by the mirror displacement profile 113 illustrated in theabove described FIG. 7J and FIG. 7L.

FIG. 7R is a diagram for illustrate the relationship between incidentlight/reflection and aperture stop when a mirror is shifted between theON, intermediate and OFF states. Specifically the mirror 718 is operatedin the ON and OFF states depicted in reverse direction for conveniencein illustration.

Specifically, FIG. 7R shows the circuit configuration of FIG. 7 asviewed from the back side.

When the mirror 718 is in the ON state, the major portion of an incidentlight 301 a is projected to the aperture stop 816 a, as reflection light301 b, to be projected.

When the mirror 718 is in a horizontal stationary state, a portion ofthe reflection light 301 b is blocked by the aperture stop 816 a. Theamount of light is reduced from the quantity of the ON state.

When the mirror 718 is in the OFF state, the reflection light 31 b iscompletely projected away from the aperture stop 816 a, and therefore areflection light 301 b is projected out of the aperture stop 816 a doesnot exist.

Therefore, the combination of the mirror displacement profiles 140,including the horizontal stationary state as illustrated in the abovedescribed FIG. 7Q, makes it possible to attain the control of thequantity of light of the reflection light 301 b that is determined bycontrolling the mirror 718 and aperture stop 816 a, to control of grayscales.

FIG. 7S is a diagram for illustrating a mirror displacement profile inthe case of applying, to a color display, a gray scale control by meansof a deflection control, including the horizontal stationary state of amirror illustrated in the above described FIG. 7Q.

FIG. 7S illustrates the case of attaining the display of a color videoimage by repeating, for three times, the respective sub-frames 101 ofthe red (R) light, green (G) light, and blue (B) light.

Specifically, the sub-frame corresponding to R applies the abovedescribed mirror displacement profile 141 to set a 100% gray scale. Thesub-frame corresponding to G applies the above described mirrordisplacement profile 142 to set a 50% gray scale. The sub-framecorresponding to B applies the above described mirror displacementprofile 143 to set a 25% gray scale, thereby attaining a color displayhaving an advantage, for example, in the brightness of R resulting frommixing R, G and B of the aforementioned respective gray scales.

Each of the circuit configurations illustrated in the above describedFIGS. 7G, 7H, and 7M comprise the memory cells M1 and M2 for controllingthe mirror 718 each has a simple DRAM structure requiring one transistorat most, and therefore the structure of the individual memory cell canbe manufactured with reduced size.

This in turn makes it easy to obtain a high level of resolution byarraying a larger number of mirror elements 700 within a certain sizedmirror element implemented as array of the mirror device 200.

Furthermore, the exemplary configuration of FIG. 7M the electrode 721 aand the electrode 721 b may be controlled by way of the plate lines 194(i.e., the second plate line 194 a and the first plate line 194 b).Specifically, significant increase of gray scales in displaying theimage may be achieved independently from the bit line 190 and word line193. Therefore, a large extension of a gray scale expression is enabled.In other words, both a high level of resolution of a projection imageand a high grade of gradation thereof can be attained.

Specifically the characteristics of the mirror element of the mirrordevice produced by the production method described by methodsillustrated according to FIGS. 5A through 5F, and the mirror element 600shown in FIGS. 6A and 6B, and the mirror element 700 shown in FIGS. 7Athrough 7S may be applied to other mirror elements.

<Single-Plate Projection Apparatus>

The following is a description of an example of the single-plateprojection apparatus that comprises one mirror device according to thepresent embodiment.

FIG. 8 is a functional block diagram for showing the configuration of asingle-plate projection apparatus that includes a mirror deviceaccording to the present embodiment.

A light source 801 emits an illumination light for projecting an image.The light source 801 is controlled by a light source control unit 802includes a processor 810. The light source 801 may comprise an arc lamplight source, a laser light source, or a light emitting diode (LED). Thelight source 801 may also implement a plurality of sub-light sources.The number and period of time for turning on each of the sub-lightsources are controlled by a light source control unit 802 to adjust thelight intensity.

Also, the light source control unit 802 controls and turns on thesub-light sources according to the integrated light intensity based onthe positions of the sub-light sources to bring forth light intensityadjustment according to the locality of the light distributions.

With the light source 801 comprises a plurality of laser light sourceswith different wavelengths, the light source control unit 802 changingover the individual laser light sources enables a selection of a colorof incident light. Therefore, this configuration does not require thecolor wheel 806 described below. Also is the light source may becontrolled to emit a pulse emission of light of a laser light source orlight emitting diode (LED) light source.

When a laser light source emits substantially-parallel flux of lightwith a small light dispersion angle an illumination light flux of theflux reflecting on the mirror device 814 has a reduced numericalaperture NA depending on the functional relationship with the etendue.The substantially-parallel fluxes can be moved closer to each other inthis configuration because an interference of the illumination lightflux prior to reflection from the mirror device can be avoided. As aresult, the mirror can have a smaller size and the deflection angle ofthe mirror can be reduced. Furthermore, the reduction of the deflectionangle of the mirror by moving the illumination light flux and projectionlight flux closer to each other makes it possible to make a projectionsystem even more compact. A first condenser lens 803 converges the lightfrom the light source 801. A rod integrator 804 uniforms an intensity oflight. A second condenser lens 805 converges the light emitted from therod integrator 804.

A color wheel 806 comprises a filter member, which includes a pluralityof filters. Each of the individual filters extracts a light of specificwavelength. For example, a filter member may include three filters,i.e., a filter for transmitting the light of the wavelength of red, onefor transmitting the light of the wavelength of green, and one fortransmitting the light of the wavelength of blue.

Furthermore, the light-passing path for each filter is controlled andswitched with a color wheel drive unit 807 rotating or sliding thefilter member. The filter may be formed to process light of a specificpolarization. The motor control unit 808 of a processor 810 controls thecolor wheel drive unit 807. The rotation or slide speed of the filter iscontrolled by the color wheel drive unit 807.

A total internal reflection (TIR) prism 809 includes an air gap betweentwo triangle prisms, i.e., a first prism 811 and a second prism 812.Additionally, the first prism 811 serves a function of totallyreflecting the incident light. For example, the first prism 811 totallyreflects the incident light to the light path entering the mirrordevice. The totally reflected light is modulated by the mirror deviceand reflected toward the second prism 812. The second prism 812transmits the reflection light projected thereto at a critical angle orsmaller and is modulated by the mirror device 814.

The mirror device 814 is enclosed in package 813. The mirror device 814is controlled by the spatial light modulator control unit 815 of theprocessor 810.

A projection lens 816 enlarges the light reflected and modulated by themirror device 814 to project the light onto a screen 817.

The processor 810 comprises a light source control unit 802, a motorcontrol unit 808, and an SLM control unit 815, for synchronouslycontrolling each of the aforementioned control units by combining them.Furthermore, the processor 810 is connected to an image signal inputunit 818 to receive and process image signal data input therefrom. Theprocessor 810 is also connected to the frame memory 819 for sending theprocessed image signal data. The image signal input unit 818 inputs theincoming image signal data to the processor 810.

Furthermore, the frame memory 819 stores the image signal data processedby the processor 810 for displaying image for a single screen.

The following is a description of the principle of projecting a colorimage at the single-plate projection apparatus 800 as shown in FIG. 8.

In the single-plate projection apparatus 800, the light emitted from thelight source 801 enters a filter of the color wheel 806 aftertransmitting through the first condenser lens 803, rod integrator 804,and second condenser lens 805.

The light of a specific wavelength is transmitted through a filter ofthe color wheel 806 and enters the first prism 811 of the total internalreflection (TIR) prism 809. Furthermore, the light reflected by thefirst prism 811 of the TIR prism 809 enters the mirror device 814enclosed in the package 813.

The light reflected on, and modulated by, the mirror element of themirror device 814 re-enters the TIR prism 809 and transmits through thesecond prism 812 of the TIR prism 809. Then, the light transmits fromthe prism is projected onto the screen 817 after transmitting throughthe projection lens 816.

In this image projection apparatus, the light source control unit 802 ofthe processor 810 controls the intensity of light, of the light sourceby applying the image signal data received from the image signal inputunit 818. In addition, the motor control unit 808 is controlled based onthe image signal data, and the color wheel drive unit 807 is controlledby the motor control unit 808. A control for changing over filters ofthe color wheel 806 is performed by the color wheel drive unit 807.Furthermore, the SLM control unit 815 applies the image signal data tocontrol a plurality of light modulation elements of the mirror device814.

The single-plate projection apparatus 800 configured as described abovedivides a period for displaying one image (i.e., one frame) intosub-frames corresponding to the individual wavelengths of light inrelation to the respective wavelengths of light, e.g., the wavelengthcorresponding to red, that corresponding to green, and thatcorresponding to blue. Furthermore, the light of each wavelength isilluminated onto the mirror device 814 in accordance with the period ofeach sub-frame. Therefore, the period of each sub-frame, the period ofmodulating the light of each wavelength at the mirror device 814 and theperiod of stopping a filter of the color wheel 806 are mutuallydependent. A selective reflection of the incident light at the mirrordevice 814 is therefore controlled for only the light of the individualwavelength reflected onto the projection light for projection onto thescreen. Additionally, a sequential projection of lights of theindividual wavelengths in accordance with the respective sub-frameperiods generates a projection of a color image.

The following is a description of an example of a multi-plate projectionapparatus implemented with a plurality of mirror devices. Themulti-plate projection apparatus comprises a plurality of light sources,a plurality of mirror devices, and a projection lens.

The light source may preferably be a laser light source or a lightemitting diode (LED). A plurality of laser light sources may beimplemented with independently controlled light sources. The independentcontrol of each light source eliminates the requirement for employing acolor filter by turning off a laser light source having a prescribedwavelength. The laser light source may also be controlled to emit lightas a pulse emission, which is difficult to achieve with a mercury lamp.

The following provides descriptions of the configurations and principlesof a two-plate projection apparatus and three-plate projectionapparatus, as examples of multi-plate projection apparatuses comprisingmirror devices according to the present embodiment.

<Two-Plate Projection Apparatus>

The two-plate projection apparatus is configured to make two mirrordevices respond respectively to two groups of light sources.Furthermore, one mirror device modulates the light from one group oflight sources and another mirror device modulates the light from anothergroup of light sources. Then, each of the mirror devices synthesizes thereflected and modulated light for projecting an image.

For example, when projecting an image with the lights of wavelengthscorresponding to three colors, i.e., red, green, and blue light, thehigh visibility green light is modulated by one mirror device. The redand blue lights are modulated by another mirror device in sequence orsimultaneously. Then, the lights modulated by the respective mirrordevices are synthesized to project an image onto a screen.

FIGS. 9A through 9D are configuration diagrams of a two-plate projectionapparatus comprising two mirror devices enclosed in one package.

The projection apparatus 900 shown in FIGS. 9A through 9D comprises agreen laser light source 901, a red laser light source 902, a blue laserlight source 903, illumination optical systems 904 a and 904 b, twotriangle prisms 906 and 909, two mirror devices 920 and 930, which arecontained and enclosed in one package 911, a circuit board 908, a jointmember 912, a light shield member 913, a light guide prism 914, and aprojection optical system 923.

The individual light sources 901, 902, and 903 are laser light sourcesas described for the single-plate system and controllable to emit lightsas pulsed emissions. The light sources may alternatively include aplurality of sub-laser light sources. The light source may use twomercury lamps corresponding to the respective mirror devices. In thecase of using the mercury lamps, a filter 905 is used for allowing onlythe light of a specific wavelength to transmit through while reflectingother light of wavelengths on the surface of synthesizing the reflectionlight in a prism 910 described later provides a similar effect as acolor filter. Alternatively, a dichroic prism or dichroic mirror may beused to separate lights of different wavelengths, and thereby the mirrordevice may be applied to modulate light of a specific wavelengthseparated by the dichroic prism or mirror. The illumination opticalsystems 904 a and 904 b are optical elements such as collector lensesand rod integrators, same as that described for the single-plateprojection apparatus, convex lenses, or concave lenses.

The prism 910 is formed by combining two triangle prisms 906 and 909,performs the function of synthesizing the reflection lights from the twomirror devices 920 and 930. When the prism 910 synthesizes thereflection lights from the individual mirror devices, a filter 905 suchas a dichroic filter, may also be used for transmitting only the lightof a specific wavelength while reflecting the other light of wavelengthson the surface of synthesizing the reflection light in a prism 910.

The filter 905 performs the same function as a color filter because of acapability of allowing a passage of only the light of a specificwavelength while reflecting the other light of wavelengths. Meanwhile,for a system uses a laser light source that emits light which has aspecific polarization direction, a polarization light beam splitterfilm, or a polarization light beam splitter coating, that performs aseparation of light or a synthesis of light by using the difference inpolarization direction of light, may be used for the synthesis surfaceof a reflection light of the prism 910.

The package 911 is similar to the package which has been described forthe single-plate projection apparatus. The package 911 as shown in FIGS.9A through 9D is configured to contain two mirror devices 920 and 930within one package 911. Alternatively, however, the mirror devices 920and 930 may be contained in separate packages.

Specifically FIGS. 9A through 9D show the mirror arrays 921 and 931, anddevice substrates 922 and 932, of the respective mirror devices 920 and930.

The circuit board 908 is connected to a processor similar to theprocessor described for the single-plate projection apparatus describedabove. The processor comprises a SLM control unit and a light sourcecontrol unit. Furthermore, the processor processes the input imagesignal data and sends data of the processed information to the SLMcontrol unit and light source control unit. The SLM control unit andlight source control unit control the mirror device and light source byway of the circuit board 908 applying the data of the processedinformation.

The mirror device and the light source are controlled to operatesynchronously. The input of the image signal data to the processor andother activities have been described for the single-plate projectionapparatus, and therefore the description is not repeated here.

The joint member 912 serves the function of joining the prism 910 to thepackage 911. The material used for the joint member 912 may, forexample, be fritted glass.

The light shield member 913 serves the function of shielding unnecessarylight. The material used for the light shield member 913 may, forexample, be graphite or may be composed of similar materials. Theprojection apparatus 900 shown in FIGS. 9A through 9D further includeslight shield member 913 on a part of the bottom of the prism 910 andalso on the rear surface of the prism 910.

The light guide prism 914 is a right-angle triangle cone prism. Theprism 914 has a sloped face adhesively attached to the front face of theprism 910 with the bottom of the light guide prism 914 facing upward.Furthermore, the light guide prism 914 is formed with an optical axis ofthe individual light sources 901, 902, and 903, the optical axis of theillumination optical systems 904 a and 904 b corresponding to therespective light sources and the optical axis of the light emitted fromthe individual light sources 901, 902, and 903 are respectivelyperpendicular to the bottom of the light guide prism 914. The lightsemitted from the individual light sources 901, 902, and 903 areprojected configuration orthogonally incident to the light guide prism914 and prism 910. As a result, the transmissivity of light can beincreased on the incidence surfaces of the light guide prism 914 andprism 910 when the respective lights emitted from the individual lightsources 901, 902, and 903 enters the light guide prism 914 and prism910.

The projection optical system 923 is an optical element for projectinglights for displaying images onto the screen. For example, the opticalelement may be a projection lens for enlarging the light for projectingan image onto the screen and the like.

Specifically, when using both a light source emitting polarized lightand a polarization beam splitter film, a two-plate projection apparatuscan be configured by implementing a ½ wavelength plate or ¼ wavelengthplate on the bottom surface of the prism 910.

The following is a description of the principle of projection of thetwo-plate projection apparatus 900 by referring to FIGS. 9A through 9D.

The projection apparatus 900 transmits the green laser light 915incident from the front direction of the prism 910, followed bytransmitting the red laser light 916 or blue laser light 917sequentially in a time division. The green laser light 915 and red laserlight 916 or blue laser light 917 is reflected to the inclined surfacedirection of the prism 910 by two mirror devices 920 and 930 of thepresent embodiment. Then, the green laser light 915 and the red laserlight 916 or blue laser light 917, which are reflected on the inclinedsurface side of the prism 910, are synthesized and the image isprojected on the screen by way of the projection optical system 923.

The following is a description of the operations of projection of imagesstarting from the incidence of the individual laser lights 915, 916, and917 from the front direction of the prism 910 until the reflection ofthe respective laser lights 915, 916, and 917 to an direction ofinclined surface of the prism 910 through two mirror devices 920 and930. The details of operation are described by referring to the frontview diagram of the two-plate projection apparatus 900 shown in FIG. 9A.

The green laser light 915 and the red laser light 916 or blue laserlight 917 are emitted respectively from the green laser light source 901and the red laser light source 902 or blue laser light source 903 andtransmitting through the illumination optical systems 904 a and 904 bcorresponding to the green laser light 915 and the red laser light 916or blue laser light 917. The light then enters into the prism 910 aftertransmitting through the light guide prism 914. Then, the green laserlight 915 and the red or blue laser light 916 or 917 transmit in theprism 910, and enters the package 911 which is joined to the bottom ofthe prism 910.

After passing through the package 911, the green laser light 915 and thered or blue laser lights 916 or 917 enter into two mirror devices 920and 930, which are contained in a single package 911 and whichcorrespond to the individual laser lights 915, 916, and 917. The lightsare modulated at the respective mirror devices 920 and 930, then theindividual laser lights 915, 916, and 917 are reflected to the inclinedsurface direction of the prism 910.

The following is a description of the operation and processes of imageprojection starting from the reflection of the individual laser lights915, 916, and 917 at the respective mirror devices 920 and 930 until theprojection of an image, by referring to the rear view diagram of thetwo-plate projection apparatus 900 shown in FIG. 9B.

A green laser ON light 918 and a red or blue laser ON light 919reflected toward the rear surface direction of the prism 910 byrespective mirror devices 920 and 930 in the ON state are re-transmittedthrough the package 911 to enter into the prism 910.

Then, the green laser ON light 918 and the red or blue laser ON light919 are reflected on the inclined surface of the prism 910. Then, thegreen laser ON light 918 is re-reflected on the film 905 fortransmitting a light only of a specific wavelength while reflecting thelight of other wavelengths. Meanwhile, the red or blue laser ON light919 is transmitted through the film 905.

Then, the green laser ON light 918 and the red or blue laser ON light919 are synthesized on the same optical path and is incident together tothe projection optical system 923 for projecting a color image.Specifically the optical axes of the respective ON lights 918 and 919emitted to the projection optical system 923 from the prism 910 arepreferably align a direction perpendicular to the emission surface ofthe prism 910.

FIG. 9C is a side view diagram showing a two-plate projection apparatuscomprising two mirror devices as described above.

The green laser light 915 emitted from the green laser light source 901enters the light guide prism 914 perpendicularly after transmittingthrough the illumination optical system 904 a. After transmittingthrough the light guide prism 914, the green laser light 915 furthertransmits through the prism 910 joined with the light guide prism 914and enters the mirror array 921 of the mirror device 920 contained inthe package 911.

The mirror array 921 reflects the incident green laser light 915according to the deflection angles of the mirror that may be controlledin one of the states. A mirror in an ON state reflects an entirereflection light to enter into the projection optical system 923 theintermediate light state in which a portion of the reflection lightenters the projection optical system 923 and the OFF light state inwhich none of the reflection light enters the projection optical system923.

A green laser light 924 when transmitting in a period of the ON lightstate is reflected from the mirror array 921 to have the entire lightenters into the projection optical system 923.

Meanwhile, a laser light 925 when transmitting in a period of theintermediate state is reflected from the mirror array 921 to have aportion of the light enters into the projection optical system 923.

Furthermore, a laser light 926 when transmitting in a period of the OFFlight is reflected from the mirror array 921 toward the light shieldlayer 913 as part of the apparatus on the rear surface of the prism 910.In addition, the reflected laser light 926 is absorbed in a light shieldlayer 913.

With this configuration, the green laser lights are projected with amaximum light intensity in the ON light. The green lights are projectedwith the intermediate light intensity between the ON light and OFF lightin the intermediate light, or at the zero light intensity in the OFFlight form is incident to the projection optical system 923.

Specifically the retention of the deflection angle of the mirror betweenthe ON light state and OFF light state create an intermediate lightstate. Furthermore, the mirror is designed and manufactured to perform afree oscillation as described above with an operation repeats thedeflection angles of the mirror at a deflection angle constituting theON state, at the angle constituting the intermediate state and at theangle constituting the OFF state. Adjustment of intensity of lightincident to the projection optical system 923 may be controlled bycontrolling the number of free oscillations.

Therefore, an image with a high grade of gray scale may be displayed bycontrolling a light intensity in the intermediate state.

A similar process on the reverse surface that is, on the side having thered laser light source 902 and blue laser light source 903 may also becarried out.

FIG. 9D is a top view diagram of a two-plate projection apparatuscomprising two mirror devices according to the present embodiment.

The light reflected from the mirror operated in an OFF light state maybe absorbed by the light shield layer 913 on the rear without beingreflected on the inclined surface of the prism 910. This may be achievedby placing the individual mirror devices 920 and 930 to form a 45-degreeangle relative to the four sides of the outer circumference of thepackage 911 on the same horizontal plane as shown in FIG. 9D.

<Three-Plate Projection Apparatus>

The following is a description of a three-plate projection apparatus.

The three-plate projection apparatus includes three mirror devices toprocess respective lights projected from three groups of light sources.The mirror devices modulate the individual lights emitted from therespective light sources. Then, the apparatus synthesizes the individuallights modulated by the respective mirror devices to project an image.

For example, when projecting an image by the lights of three colors,i.e., red light, green light, and blue light, the individual lights arecontinuously modulated by three respective mirror devices, and themodulated individual lights are synthesized for projecting a colorimage.

FIG. 10 is a functional block diagram for showing the configuration of athree-plate projection apparatus comprising three mirror devices,according to the present embodiment, which are contained in therespective packages.

The projection apparatus 1000 shown in FIG. 10 comprises a light source1001, a first condenser lens 1002, a rod integrator 1003, a secondcondenser lens 1004, a third condenser lens 1005, a TIR prism 1008, afirst dichroic prism 1009, a second dichroic prism 1010, a third prism1011, individual mirror devices 1012, 1013, and 1014, and individualpackages 1015, 1016, and 1017 contain the respective mirror devices1012, 1013, and 1014, and a projection lens 1018.

The light source 1001 may be implemented with a mercury lamp source, alaser light source, an LED, or similar light sources, as in the case ofthe light source described for the single-plate projection apparatus andtwo-plate projection apparatus as describe above. The configuration andoperation of the light source, such as the sub-light source and lightsources for pulsed emission, are similar to the light source for theprojection apparatuses described above and therefore the description isnot provided here.

Similar to those described for the single-plate projection apparatus,the first condenser lens 1002, rod integrator 1003, second condenserlens 1004, and third condenser lens 1005 sere the function of condensingthe light. Meanwhile, the rod integrator 1003 carries out a function ofevening out a light intensity.

The TIR prism 1008 is similar to the above-described prism for thesingle-plate projection apparatus and therefore the description is notprovided here. Specifically the TIR prism 1008 used for the three-plateprojection apparatus shown in FIG. 10 includes a first prism 1006 and asecond prism 1007.

The first dichroic prism 1009 and second dichroic prism 1010 are prismstransmitting only the light of a specific wavelength through the prismwhile reflecting the light of other wavelengths. Furthermore, the thirdprism 1011 is a common prism. Specifically the first dichroic prism 1009and second dichroic prism 1010 may be configured by respective dichroicmirrors.

For example, FIG. 10 shows the first dichroic prism 1009 as a prismreflecting only the light of the wavelength equivalent to red whiletransmitting through the light of other wavelengths and the seconddichroic prism 1010 as a prism reflecting only the light of thewavelength equivalent to blue while transmitting through the light ofother wavelengths. In addition, the drawing shows the case ofconfiguring the third prism 1011 as a prism making the light of thewavelength equivalent to green travel straight.

The individual packages 1015, 1016, and 1017 enclose and contain therespective mirror devices 1012, 1013, and 1014.

The projection lens 1018 serves the function of enlarging individuallights synthesized after the individual lights are reflected andmodulated at the respective mirror devices 1012, 1013, and 1014.

A processor 1020 is basically similar to the one described for thesingle plate projection apparatus, and comprises a spatial lightmodulator control unit 1021 and a light source control unit 1022.Furthermore, the processor 1020 processes the input image signal data asthat described above for the single plate projection apparatus.

The spatial light modulator control unit 1021 as shown here is basicallysimilar to the one described for the single plate projection apparatus.The processor 1021 is connected to the individual mirror devices 1012,1013, and 1014. Furthermore, the spatial light modulator control unit1021 is capable of controlling the individual mirror devices 1012, 1013,and 1014 independently or synchronously on the basis of the image signaldata processed by the processor. The processor also controls theindividual mirror devices 1012, 1013, and 1014 synchronously with otherconstituent members.

The light source control unit 1022 shown here is similar to the onedescribed for the single plate projection apparatus, is connected to thelight source 1001 for controlling the light intensity of the lightsource, for controlling and turning on selected sub-light sources, andto carry out similar functions, on the basis of the image signalprocessed by the processor.

Frame memory 1023 and an image signal input unit 1024 are similar to theones described for the single plate projection apparatus and thereforethe description is not repeated here.

The following is a description of the operation and processes ofprojection of a color image at the three-plate projection apparatus 1000shown in FIG. 10.

In the three-plate projection apparatus 1000, the light emitted from thelight source 1001 is transmitted sequentially through the firstcondenser lens 1002, rod integrator 1003, second condenser lens 1004,and third condenser lens 1005. Then the light is incident to the firstprism 1006 of the TIR prism 1008 at an angle equal to or greater than acritical angle. Then, the incident light is totally reflected by thefirst prism 1006 of the TIR prism 1008.

The totally reflected light enters the first dichroic prism 1009.Furthermore, while the light of other wavelengths are passed, only thelight of the wavelength equivalent to red, among the totally reflectedlight, is reflected from the light emission surface of the firstdichroic prism 1009 and/or on the light incident surface of the seconddichroic prism 1010.

Then, as for the light incident to the second dichroic prism 1010, onlythe light of the light with a blue wavelength among the incident lights,is reflected, while the light of other wavelength, that is, the greenlight, is transmitted through the light emission surface of the seconddichroic prism 1010 and/or the light incident surface of the third prism1011.

The light which enters the third prism 1011, and from which the bluelight and red light wavelengths are removed and the green lighttransmits through the third prism 1011.

Then, the lights spectrally divided to individual wavelengths areincident, respectively to the packages 1015, 1016, and 1017, whichcontain the respective mirror devices 1012, 1013, and 1014 and which areplaced on the respective side faces of the first dichroic prism 1009,second dichroic prism 1010, and third prism 1011.

The individual lights transmitted through the packages 1015, 1016, and1017 enter the respective mirror devices 1012, 1013, and 1014 of thepresent embodiment. Here, the individual mirror devices 1012, 1013, and1014 are independently controlled by the spatial light modulator controlunit 1021 to respond to the respective lights according to the imagesignal processed by the processor 1020. The individual mirror devices1012, 1013, and 1014 modulate, and reflect, the incident respectivelights.

Then, the red light reflected by the mirror device 1012, re-enters thefirst dichroic prism 1009. Also, the blue light reflected by the mirrordevice 1014, re-enters the second dichroic prism 1010. Furthermore, thegreen light reflected by the mirror device 1013, re-enters the thirdprism 1011.

The red light re-enters into the first dichroic prism 1009, and the bluelight re-entered the second dichroic prism 1010, repeating a number oftimes of reflections in the respective prisms 1009 and 1010.

Then, the blue light overlaps its optical path with that of the greenlight re-entered the second dichroic prism 1010 from the third prism1011, and the blue light and green light are thereby synthesized.

Then, the light synthesized light of the green and blue lights entersthe first dichroic prism 1009 from the second dichroic prism 1010.

Then, the red light overlaps the optical path with that of thesynthesized light of green and blue lights entered the first dichroicprism 1009 from the second dichroic prism 1010, and these lights arethereby synthesized.

The synthesized light of the three individual lights modulated by therespective mirror devices 1012, 1013, and 1014 enters the second prism1007 of the TIR prism 1008 at an angle equal to or smaller than thecritical angle.

Then, the synthesized light is transmitted through the second prism 1007of the TIR prism 1008 and is projected to the screen 1019 aftertransmitting through the projection lens 1018.

According to above-described optical processes, a color image can beprojected at the three-plate projection apparatus.

In such a configuration, as compared to the single-plate image displaysystem described above, there will be no visual problem caused by a“color breakup,” phenomenon since each light of the primary colors isdisplayed at all times. Furthermore, more effective and continuousprojection of emitted light from the light source provides would inprinciple display a brighter image compared with the single-panelprojection apparatus.

Although the present invention has been described in terms of thepresently preferred embodiment, it is to be understood that suchdisclosure is not to be interpreted as limiting. Various alternationsand modifications will no doubt become apparent to those skilled in theart after reading the above disclosure. Accordingly, it is intended thatthe appended claims be interpreted as covering all alternations andmodifications as fall within the true spirit and scope of the invention.

1. A mirror device, comprising: an electrode placed on a substrate; amemory circuit connected to the electrode; an elastic hinge disposednear said electrode and extending from said substrate for supporting amirror above said electrode wherein said elastic hinge having a negativetemperature coefficient of resistance.
 2. The mirror device according toclaim 1, wherein: the elastic hinge further comprises a silicon materialcontaining at least an additive selected from materials consist ofeither a group-III atom or a group-V atom.
 3. The mirror deviceaccording to claim 1, wherein: the elastic hinge further comprises asilicon material containing an additive and having a resistanceapproximately 1 giga-ohms or less.
 4. The mirror device according toclaim 1, wherein: the elastic hinge is formed by applying a chemicalvapor deposition (CVD) fabrication process on said substrate.
 5. Themirror device according to claim 1, wherein: the elastic hinge furthercomposed of a metallic material migrating from said electrode or mirror.6. The mirror device according to claim 1, wherein: the elastic hingehas smaller cross-sectional area near said mirror than a cross sectionalarea of an opposite end near said substrate.
 7. A mirror device,comprising: a stationary electrode disposed on a substrate; a movableelectrode disposed at a distance away from the stationary electrode; anelastic hinge extended from said substrate for supporting the movableelectrode; and a drive circuit for applying adjustable voltages to thestationary electrode or movable electrode to control the movableelectrode, wherein the drive circuit controls the movable electrode tooperate with a time sequence depending on an electric resistance of theelastic hinge.
 8. The mirror device according to claim 7, wherein: thetiming of the drive circuit controls the time sequence of an operationof the movable electrode is when the distance between fixed electrodeand the movable electrode is minimum and start moving apart with eachother.
 9. The mirror device according to claim 7, wherein: the elastichinge further comprises a silicon (Si) material doped with a materialselected from a group of materials consisted of E either of a group-IIIatom and group-V atom.
 10. The mirror device according to claim 7,further comprising: an anti-stiction coating applied to cover at leasteither of the movable electrodes or stationary electrode for preventinga stiction of a mirror to either said movable electrode or saidstationary electrode.
 11. A mirror device, comprising: a plurality ofelectrodes placed on a substrate; a mirror placed at a distance awayfrom the electrode; and an elastic hinge disposed between the mirror andelectrode, wherein the elastic hinge has a smaller resistance in anoperational temperature or operating the mirror device than a normalambient temperature.
 12. The mirror device according to claim 1,wherein: the operational temperature for operating the mirror device isapproximately 50° C. or higher and the electric resistance of theelastic hinge is approximately 0.5 giga-ohms or less.